SCHEDULE 14A INFORMATION
                                 (Rule 14a-101)

           Proxy Statement Pursuant to Section 14(a) of the Securities
                              Exchange Act of 1934
Filed by the Registrant |X|

Filed by a Party other than the Registrant |_|

Check the appropriate box:

|X| Preliminary Proxy Statement                  |_| Confidential, for Use of
|_| Definitive Proxy Statement                       the Commission Only (as
|_| Definitive Additional Materials                  permitted by Rule
|_| Soliciting Material Pursuant to Rule 14a-12      14a-6(e)(2))

                              REPLIGEN CORPORATION
                (Name of Registrant as Specified in Its Charter)

--------------------------------------------------------------------------------
    (Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of filing fee (Check the appropriate box):

|X| No fee required.
|_| Fee computed on table below per Exchange Act Rules 14a-6(i)(4) and 0-11.

      (1)   Title of each class of securities to which transaction applies:
                                 NOT APPLICABLE

      (2)   Aggregate number of securities to which transactions applies:
                                 NOT APPLICABLE

      (3)   Per unit price or other underlying value of transaction computed
            pursuant to Exchange Act Rule 0-11 (Set forth the amount on which
            the filing fee is calculated and state how it was determined):
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previously. Identify the previous filing by registration statement number, or
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                              Repligen Corporation
                           41 Seyon Street, Building 1
                                Waltham, MA 02453
                                 (781-250-0111)

                    NOTICE OF ANNUAL MEETING OF STOCKHOLDERS


To the Stockholders:

         The Annual Meeting of Stockholders of Repligen Corporation, a Delaware
Corporation ("Repligen" or the "Company") will be held on Wednesday, September
10, 2003, 10:00 a.m. local time, at the offices of Repligen, 41 Seyon Street,
Building 1, Waltham, Massachusetts for the following purposes:


1.    To elect a Board of Directors for the ensuing year;

2.    To consider and act upon a proposal to increase the size of the Board of
      Directors to eight members;

3.    To elect Thomas F. Ryan, Jr. to fill one of the vacancies on the Board of
      Directors, if Proposal 2 is approved by the Stockholders;

4.    To consider and act upon a proposal to amend the Company's by-laws to
      allow the Board of Directors to set the size of the Company's Board of
      Directors and to appoint Directors to fill any vacancy until the next
      Annual Meeting;

5.    To consider and act upon a proposal to amend the 2001 Repligen Corporation
      Stock Option Plan, to increase both the number of options the Company
      automatically grants per year and the aggregate number of options granted
      to its non-employee directors;

6.    To consider and act upon a proposal to amend and restate the 2001 Repligen
      Corporation Stock Option Plan, to allow shares of restricted stock to be
      awarded under such plan;

7.    To ratify the selection of Ernst & Young LLP as the independent auditors
      of Repligen for the fiscal year ending March 31, 2004; and

8.    To transact such other business as may properly come before the Annual
      Meeting and any adjournments or postponements thereof.

         Stockholders entitled to notice of and to vote at the Annual Meeting
shall be determined as of the close of business on July 14, 2003, the record
date fixed by the Board of Directors for such purpose.

                                            By Order of the Board of Directors

                                            Daniel P. Witt, Secretary
Waltham, Massachusetts
July  , 2003



--------------------------------------------------------------------------------
IT IS IMPORTANT THAT YOUR SHARES BE REPRESENTED AT THE MEETING. WHETHER OR NOT
YOU PLAN TO ATTEND THE MEETING IN PERSON, YOU ARE REQUESTED TO COMPLETE, SIGN,
DATE AND MAIL PROMPTLY THE ENCLOSED PROXY WHICH IS BEING SOLICITED ON BEHALF OF
THE BOARD OF DIRECTORS. A RETURN ENVELOPE WHICH REQUIRES NO POSTAGE IF MAILED IN
THE UNITED STATES IS ENCLOSED FOR THAT PURPOSE. YOU MAY ALSO VOTE BY TELEPHONE
OR VIA THE INTERNET IN ACCORDANCE WITH THE INSTRUCTIONS LISTED ON THE PROXY
CARD.
--------------------------------------------------------------------------------



                              REPLIGEN CORPORATION
                           41 SEYON STREET, BUILDING 1
                                WALTHAM, MA 02453

                                   ----------

                                 PROXY STATEMENT
                     FOR THE ANNUAL MEETING OF STOCKHOLDERS
                        TO BE HELD ON SEPTEMBER 10, 2003

                                   ----------

                                                 , 2003

      Proxies in the form included with this proxy statement are solicited by
the Board of Directors (the "Board") of Repligen Corporation, a Delaware
corporation ("Repligen" or the "Company"), for use at the Annual Meeting of
Stockholders of Repligen to be held, pursuant to the accompanying Notice of
Annual Meeting, on Wednesday, September 10, 2003, 10:00 a.m. local time, or at
any adjournments or postponements thereof (the "Annual Meeting" or the
"Meeting"), at Repligen's principal executive offices at 41 Seyon Street,
Building 1, Waltham, Massachusetts 02453. Only stockholders of record as of July
14, 2003 (the "Record Date") will be entitled to notice of and to vote at the
Meeting and any adjournments or postponements thereof. As of the Record Date,
________ shares of Common Stock, $.01 par value (the "Common Stock"), of
Repligen were issued and outstanding and entitled to vote.

      Repligen's Annual Report to Stockholders, containing financial statements
for the fiscal year ended March 31, 2003, is being provided together with this
proxy statement to all stockholders entitled to vote. It is anticipated that
this proxy statement and the accompanying proxy will be first provided to
stockholders on or about , 2003.

      The holders of Common Stock are entitled to one vote per share on any
proposal presented at the Annual Meeting. Stockholders may vote in person or by
proxy. Stockholders may vote by proxy by completing, signing, dating and
returning the accompanying proxy card or by voting by telephone or via the
internet in accordance with the instructions listed on the proxy card. Execution
of a proxy will not in any way affect a stockholder's right to attend the Annual
Meeting and vote in person. Any proxy given pursuant to this solicitation may be
revoked by the person giving it any time before the taking of the vote at the
Annual Meeting. Proxies may be revoked by: (1) filing with the Secretary of
Repligen, before the taking of the vote at the Annual Meeting, a written notice
of revocation bearing a later date than the proxy; (2) duly executing a
later-dated proxy relating to the same shares and delivering it to the Secretary
of Repligen or by telephone or internet, in accordance with the instructions
listed on the proxy card, before the taking of the vote at the Annual Meeting;
or (3) attending the Annual Meeting and voting in person (although attendance at
the Annual Meeting will not in and of itself constitute a revocation of a
proxy). For those stockholders who submit a proxy by telephone or via the
internet, the date on which the proxy is submitted in accordance with the
instructions listed on the proxy card is the date of the proxy. Any written
notice of revocation or subsequent proxy should be sent so as to be delivered to
Repligen Corporation, 41 Seyon Street, Building 1, Waltham, Massachusetts 02453,
Attention: Secretary, at or before the taking of the vote at the Annual Meeting.

      Each of the persons named as attorneys in the proxies is a director and/or
officer of Repligen. All properly executed proxies returned in time to be
counted at the Annual Meeting will be voted as stated below under the heading
"Voting Procedures." Any stockholder submitting a proxy has the right to
withhold authority to vote for any individual nominee to the Board by writing
that nominee's name on the space provided on the proxy, by checking the box next
to the name of such individual if voting by proxy via the internet or, if using
the telephone to vote by proxy, by following the verbal instructions for
entering the two digit number appearing on the proxy card immediately before the
name of such individual. In addition to the election of Directors, stockholders
will consider and vote upon a proposal to ratify the selection of auditors and
will consider and vote upon proposals to increase the size of the Board, to
elect an additional person to the Board of Directors to fill one of the
vacancies created upon the approval of the proposal to increase the size of the
Board, to amend Repligen's by-laws and amend and restate the 2001 Repligen
Corporation Stock Option Plan, as further described in this proxy statement.
Where a choice has been specified on the proxy with respect to a matter, the
shares represented by the proxy will be voted in accordance with the
specifications and will be voted FOR if no specification is indicated, as
permitted by applicable regulations and by Repligen's corporate documents.

         The Board knows of no other matters to be presented at the Annual
Meeting. If any other matter should be presented at the Annual Meeting upon
which a vote properly may be taken, shares represented by all proxies received
by the Board will be voted with respect thereto in accordance with the judgment
of the persons named as attorneys in the proxies.


                                     - 1 -


                                VOTING PROCEDURES

      The representation, in person or by proxy, of at least a majority of the
outstanding shares of Common Stock entitled to vote at the Annual Meeting is
necessary to constitute a quorum for the transaction of business. Shares
represented by proxies pursuant to which votes have been withheld from any
nominee for director, or which contain one or more abstentions or broker
"non-votes," are counted as present or represented for purposes of determining
the presence or absence of a quorum for the Annual Meeting. A "non-vote" occurs
when a broker or other nominee holding shares for a beneficial owner votes on
one proposal, but does not vote on another proposal because the broker does not
have discretionary voting power and has not received instructions from the
beneficial owner.

      Election of Directors (Proposal 1). Directors are elected by plurality of
the votes cast, in person or by proxy, at the Annual Meeting. The five nominees
who receive the highest number of affirmative votes of the shares present or
represented and voting on the election of directors at the Annual Meeting will
be elected to the Board of Directors. Shares present or represented and not so
marked as to withhold authority to vote for a particular nominee will be voted
in favor of a particular nominee and will be counted toward such nominee's
achievement of a plurality. Shares present at the meeting or represented by
proxy where the stockholder properly withholds authority to vote by marking the
"WITHHOLD" box on the proxy for such nominee will not be counted toward such
nominee's achievement of plurality.

      Amendment of the 2001 Repligen Corporation Stock Option Plan. Approval of
Proposal 5 to amend the 2001 Repligen Corporation Stock Option Plan to increase
both the number of options the Company automatically grants per year and the
aggregate number of options granted to its non-employee directors will require
the approval by a majority of the holders of Common Stock of Repligen.

      Other Matters. For all other matters being submitted to stockholders at
the Annual Meeting (Proposals 2, 3, 4, 6, 7 and 8), the affirmative vote of the
majority of shares present, in person or represented by proxy, and voting on
that matter is required for approval. Shares voted to abstain are included in
the number of shares present or represented and voting on each matter. Shares
subject to broker "non-votes" are considered to be not entitled to vote for the
particular matter and have the practical effect of reducing the number of
affirmative votes required to achieve a majority for such matter by reducing the
total number of shares from which the majority is calculated.

      Laura Whitehouse will serve as the Inspector of Elections and will count
all votes and ballots.

                     PRINCIPAL HOLDERS OF VOTING SECURITIES

      The following table sets forth, as of June 30, 2003, or otherwise set
forth in the footnotes below, the name of each person who, to Repligen's
knowledge based upon representations or publicly available filings, beneficially
owned more than 5% of the shares of Common Stock of Repligen outstanding at such
date, the number of shares beneficially owned by each of these persons, and the
percentage of the outstanding shares of the Company beneficially owned by each
of these persons.


Name and Address of                    Amount and Nature of          Percent of
 Beneficial Owner                    Beneficial Ownership (1)         Class (2)
-------------------                  ------------------------       -----------
The Riverview Group, LLC...........          2,500,000                 8.37%
666 Fifth Ave, 8th Floor
New York, NY  10103

BVF Partners L.P. (3) .............          2,329,763                 7.81%
333 West Wacker Drive
Chicago, IL 60606


                                     - 2 -


--------------
(1)   Beneficial ownership, as such term is used herein, is determined in
      accordance with Rule 13d-3(d)(1) promulgated under the Securities Exchange
      Act of 1934 and includes voting and/or investment power with respect to
      shares of Common Stock of Repligen. Unless otherwise indicated, the named
      person possesses sole voting and investment power with respect to the
      shares. The shares shown include shares issuable pursuant to options or
      warrants held by the named person that may be exercised within 60 days of
      the dates indicated below.

(2)   Percentages of ownership are based upon 29,857,073 shares of Common Stock
      issued and outstanding as of June 30, 2003 or as otherwise indicated in
      the respective footnotes. Shares of Common Stock that may be acquired
      pursuant to options or warrants that are exercisable within 60 days of
      such date are deemed outstanding for computing the percentage ownership of
      the person holding such options or warrants, but are not deemed
      outstanding for the percentage ownership of any other person.

(3)   Based solely on a Schedule 13G/A filed on May 28, 2003, Biotechnology
      Value Fund, L.P. ("BVF") shares voting and dispositive power over the
      shares of the Common Stock it beneficially owns with BVF Partners L.P.
      ("Partners"). Biotechnology Value Fund II, L.P. ("BVF2") also shares
      voting and dispositive power over the shares of the Common Stock it
      beneficially owns with Partners. BVF Investments, L.L.C. ("Investments")
      (of which Ziff Asset Management, L.P. is the majority member) also shares
      voting and dispositive power over the shares of the Common Stock it
      beneficially owns with Partners. Investments 10, L.L.C. ("Investments 10")
      shares voting and dispositive power over the shares of the Common Stock it
      owns with Partners. Partners and BVF Inc. share voting and dispositive
      power over the shares of the Common Stock owned or beneficially owned by
      BVF, BVF2, Investments and Investments 10. The percent of class
      beneficially owned is as reported in such Schedule 13G/A. As of May 22,
      2003, securities beneficially owned by BVF Inc. consist of the following:

            a)    743,063 shares of Common Stock owned by BVF,

            b)    496,179 shares of Common Stock owned by BVF2,

            c)    1,005,221 shares of Common Stock owned by Investments, and

            d)    85,300 shares of Common Stock owned by Investments 10.

                                   PROPOSAL 1
                              ELECTION OF DIRECTORS

      The number of directors is currently fixed at five. There are six nominees
for director, of which five are currently directors of Repligen and one of which
has been nominated by the Nominating Committee for election if Proposal 2 to
increase the size of the Board is approved by the stockholders. The five
nominees who are existing directors are Walter C. Herlihy, Ph.D., Robert J.
Hennessey, G. William Miller, Alexander Rich, M.D. and Paul Schimmel, Ph.D.
Thomas F. Ryan, Jr. will be nominated for election upon the approval of Proposal
2.



                                    Year Nominee First
           Nominee's Name           Became A Director               Position(s) with the Company
           --------------           ------------------              ----------------------------
                                                    
    Walter C. Herlihy, Ph.D.               1996           President, Chief Executive Officer and Director
    Robert J. Hennessey                    1998           Director
    G. William Miller                      1982           Director
    Alexander Rich, M.D.                   1981           Director, Co-Chairman of the Board
    Thomas F. Ryan, Jr.                     N/A           Nominee for Director
    Paul Schimmel, Ph.D.                   1981           Director, Co-Chairman of the Board



                                     - 3 -


      The directors of the Company will be elected to hold office until the next
annual meeting of stockholders and until their successors have been duly elected
and qualified, or until their earlier death, resignation or removal.

      Shares represented by all proxies received by the Board and not marked or
voted so as to withhold authority to vote for any individual director or for any
group of directors will be voted (unless one or more nominees are unable or
unwilling to serve) for the election of the nominees named above, other than Mr.
Ryan. Mr. Ryan will elected upon the affirmative vote of the majority of shares
present, in person or represented by proxy, provided that a vacancy is created
on the Board as a result of the stockholders approving Proposal 2. The Board
knows of no reason why any nominee should be unable or unwilling to serve, but
if any nominee should be unable or unwilling to serve, proxies will be voted or
withheld in accordance with the judgment of the persons named as attorneys in
the proxies with respect to the directorship for which that nominee was unable
or unwilling to serve.

      The Board unanimously recommends a vote FOR each of the nominees for
election as directors.

                 Occupations Of Directors And Executive Officers

      Repligen's executive officers are appointed on an annual basis by, and
serve at the discretion of, the Board. Each executive officer is a full-time
employee of Repligen. The directors and executive officers of Repligen are as
follows:


        Name                        Age              Positions
        ----                        ---              ---------

Walter C. Herlihy, Ph.D. (3).....    51    President, Chief Executive Officer
                                           and Director

James R. Rusche, Ph.D............    49    Senior Vice President, Research and
                                           Development

Daniel P. Witt, Ph.D.............    56    Vice President, Business Development

Robert J. Hennessey (2)(4).......    61    Director

G. William Miller (1)(2)(3)(4)...    78    Director

Alexander Rich, M.D (2)..........    78    Director

Thomas F. Ryan, Jr. (5) .........    62    Nominee for Director

Paul Schimmel, Ph.D. (1)(3)......    62    Director

--------------
(1)   Member of the Compensation Committee

(2)   Member of the Audit Committee

(3)   Member of the Executive Committee

(4)   Member of the Nominating Committee

(5)   Intends to serve as a member of the Audit Committee

                            Biographical Information

Walter C. Herlihy, Ph.D. joined Repligen in March 1996 as President, Chief
Executive Officer and Director in connection with Repligen's merger with Glycan
Pharmaceuticals, Inc. From July 1993 to March 1996, Dr. Herlihy was the
President and CEO of Glycan Pharmaceuticals, Inc. From October 1981 to June
1993, he held numerous research positions at Repligen, most recently as Senior
Vice President, Research and Development. Dr. Herlihy holds an A.B. degree in
chemistry from Cornell University and a Ph.D. in chemistry from MIT.

James R. Rusche, Ph.D. became Senior Vice President, Research and Development in
January 2003. Dr. Rusche joined Repligen in March 1996 as Vice President,
Research and Development in connection with Repligen's merger with Glycan
Pharmaceuticals, Inc. From July 1994 to March 1996, Dr. Rusche was Vice
President, Research and Development of Glycan Pharmaceuticals, Inc. From
February 1985 to June 1994, he held numerous research positions at Repligen,
most recently as Vice President, Discovery Research. Dr. Rusche holds a B.S.
degree in microbiology from the University of Wisconsin, LaCrosse and a Ph.D. in
immunology from the University of Florida.

Daniel P. Witt, Ph.D. joined Repligen in March 1996 as Vice President, Business
Development in connection with Repligen's merger with Glycan Pharmaceuticals,
Inc. From October 1993 to March 1996, Dr. Witt was Vice President, Business
Development of Glycan Pharmaceuticals, Inc. From April 1983 to September 1993,
he held numerous research positions at Repligen, most recently as Vice


                                     - 4 -


President, Technology Acquisition. Dr. Witt holds a B.A. degree in chemistry
from Gettysberg College and a Ph.D. in biochemistry from the University of
Vermont.

Robert J. Hennessey has served as a director of Repligen since July 1998. Mr.
Hennessey served as Chief Executive Officer and President of the Genome
Therapeutics Corporation, a biotechnology company from March 1993 until October
2000 and Chairman of the Board from May 1994 through May 2003 when he stepped
down as Chairman of the Board. From 1990 to 1993, Mr. Hennessey served as the
President of Hennessey & Associates Ltd., a strategic consulting firm to
biotechnology and healthcare companies. Prior to 1990, Mr. Hennessey held a
variety of management positions at Merck, SmithKline, Abbott and Sterling Drug.
Mr. Hennessey is also a director of PenWest Pharmaceuticals and Genome
Therapeutics Corporation.

G. William Miller has served as a Director of Repligen since January 1982. Mr.
Miller is the Chairman of the Board of G. William Miller & Co., Inc., a private
merchant-banking firm. He has served in that capacity for over five years. From
January 1990 until February 1992, Mr. Miller was Chairman and Chief Executive
Officer of Federated Stores, Inc., an owner and operator of retail department
stores, supermarkets and real estate interests. Mr. Miller is a former Chairman
of the Board of Governors of the Federal Reserve System and served as Secretary
of the Treasury under President Carter. Mr. Miller is a director of the Simon
Property Group, Inc., a real estate investment trust, and GS Industries, Inc., a
producer of steel and related products. Mr. Miller is the Chairman of The H.
John Heinz Center for Science, Economics and the Environment, and Trustee of the
Marine Biological Laboratory.

Alexander Rich, M.D., Co-Founder and Co-Chairman of the Board of Directors of
Repligen, has been on the faculty of MIT since 1958 and is the Sedgwick
Professor of Biophysics. Internationally recognized for his contributions to the
molecular biology of nucleic acids, he has determined their three-dimensional
structure and has investigated their activity in biological systems. He is
widely known for his work in elucidating the three-dimensional structure of
transfer RNA, which is a component of the protein synthesizing mechanism and for
his discovery of a novel, left-handed form of DNA. He is a member of the
National Academy of Sciences, the American Philosophical Society, the Pontifical
Academy of Sciences, Rome and a foreign member of the French Academy of
Sciences, Paris. Dr. Rich has been a Director of Repligen since March 1981. Dr.
Rich is a director of Alkermes, Inc.

Thomas F. Ryan Jr., Nominee to the Board of Directors of Repligen. Mr. Ryan is
currently a private investor. Mr. Ryan served as the President and Chief
Operating Officer of the American Stock Exchange from October 1995 to April
1999. Prior to 1995, he held a variety of positions at the investment banking
firm of Kidder, Peabody & Co., Inc., serving as the firm's Chairman in 1995. He
holds a bachelor's degree from Boston College and is a graduate of the Boston
Latin School. Mr. Ryan is a Director for the New York State Independent System
Operator, a Trustee for the Brigham and Women's Hospital, a Trustee for Boston
College and a Director for Mellon Asset Management.

Paul Schimmel, Ph.D., Co-Founder and Co-Chairman of the Board of Directors of
Repligen, has been on the faculty of the Skaggs Institute of Chemical Biology at
Scripps Research Institute since 1997. He is well known for his work in
biophysical chemistry and molecular biology. His field of specialty is the
mechanism of action of proteins and the manner in which they act upon the
nucleic acids in the cell. This work involves broad applications of recombinant
DNA technology. He is a member of the National Academy of Sciences, received the
1978 ACS/Pfizer award for excellence in enzyme research, and is co-author of a
widely read textbook on biophysical chemistry. He also previously served as the
Chairman, Director of Biological Chemistry, American Chemical Society. Dr.
Schimmel has been a Director of Repligen since March 1981. Dr. Schimmel is a
director of Alkermes, Inc.

                 CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

         On May 1, 2003, Repligen sold 2,500,000 shares of Common Stock to The
Riverview Group, LLC for aggregate consideration of $12,500,000 in a private
placement, pursuant to a stock purchase agreement by and between The Riverview
Group, LLC and Repligen. Until December 31, 2003, prior to selling any shares of
Common Stock to institutional investors in a private placement, Repligen is
required to offer to The Riverview Group, LLC (and affiliated persons) 25% of


                                     - 5 -


the Common Stock proposed to be offered to institutional investors in a private
placement and to keep such offer open for ten (10) business days before
proceeding with such sale. Rodman & Renshaw, Inc. acted as the placement agent
for the transaction and Repligen paid them approximately $625,000 for its
services.

      Immediately prior to the above-referenced transaction, The Riverview
Group, LLC did not own any shares of our common stock. Pursuant to the
above-referenced transaction, The Riverview Group became an owner of 8.37% of
our common stock. Except as noted above and based on representations by The
Riverview Group, LLC, to the best of Repligen's knowledge, The Riverview Group,
LLC has not had a material relationship with Repligen or any of our affiliates
within the three-year period ending on June 30, 2003.

      No family relationship exists among the officers and directors of
Repligen.

         INFORMATION REGARDING THE BOARD OF DIRECTORS AND ITS COMMITTEES

      The Board of Directors of the Company met five times during the fiscal
year ended March 31, 2003. During the fiscal year ended March 31, 2003, no
director attended fewer than 75% of the aggregate of (i) the total number of
meetings of the Board and (ii) the total number of meetings held by all
committees of the Board on which such director served.

      The Board has a standing Audit Committee, Compensation Committee,
Executive Committee and Nominating Committee.

      The Audit Committee, currently consisting of Mr. Miller, Mr. Hennessey and
Dr. Rich, is responsible for determining the adequacy of Repligen's internal
accounting and financial controls. The Audit Committee met four times with
management and Repligen's independent public accountants to review financial
matters, quarterly results, the impact and application of the Sarbanes-Oxley Act
and matters pertaining to both the 2002 and 2003 fiscal year audits. No member
of the Audit Committee is a member of Repligen's management.

      The Compensation Committee, currently consisting of Dr. Schimmel and Mr.
Miller, is responsible for reviewing matters pertaining to the compensation of
Repligen's officers and the granting of stock options (other than stock options
which are automatically granted to certain members of the Board pursuant to
Repligen's stock option plan). See "Compensation of Directors" and "Compensation
Committee Report to Stockholders." The Compensation Committee met once during
the fiscal year ended March 31, 2003. No member of the Compensation Committee is
a member of Repligen's management.

      The Executive Committee, currently consisting of Mr. Miller, Dr. Schimmel
and Dr. Herlihy (an employee of Repligen), is authorized to exercise certain
powers of the Board not specifically reserved to the Board by Repligen's by-laws
or the General Corporation Law of the State of Delaware.

      The Nominating Committee, currently consisting of Mr. Miller and Mr.
Hennessey, is responsible for identifying, reviewing and evaluating candidates
to serve as directors of Repligen and to recommend such candidates to the Board.
The Nominating Committee was formed in June 2002 and has been actively searching
for new candidates to serve as directors, but did not formally meet during the
last fiscal year. In July 2003, the Nominating Committee met and formally
nominated Mr. Ryan to fill the vacancy created if Proposal 2 is approved by the
stockholders. The Nominating Committee may, in its discretion, consider
potential candidates for membership on the Board that have been recommended by
stockholders. Any stockholder wishing to recommend a potential candidate should
submit a recommendation in writing to Repligen's Secretary indicating the
nominee's name, qualifications and other relevant biographical information and
providing confirmation of the nominee's consent to serve as a director if
nominated and elected. No member of the Nominating Committee is a member of
Repligen's management.

               STOCK OWNERSHIP OF DIRECTORS AND EXECUTIVE OFFICERS

      The following table sets forth certain information as of June 30, 2003
with respect to beneficial ownership of shares of Repligen's Common Stock by all
directors and executive officers named in the Summary Compensation Table set


                                     - 6 -


forth below under "Summary of Executive Compensation" individually,
and by all directors and executive officers of Repligen as a group.



                                           Amount and Nature of
Beneficial Owner                         Beneficial Ownership (1)    Percent of Class (2)
----------------                         ------------------------    --------------------
                                                                       
Paul Schimmel, Ph.D. (3)...............            737,682                   2.47%
Alexander Rich, M.D. (4)...............            470,700                   1.57%
G. William Miller (5)..................            134,000                     *
Robert J. Hennessey (6)................             54,000                     *
Thomas F. Ryan, Jr. ...................             10,000                     *
Walter C. Herlihy (7)..................            770,668                   2.53%
James R. Rusche (8)....................            278,758                     *

Daniel P. Witt (9).....................            211,668                     *
All directors, nominees and executive
 officers as a group (8 persons) (10)..          2,455,808                   7.93%


--------------
* Less than one percent

(1)   Unless otherwise indicated, the named person possesses sole voting and
      investment power with respect to the shares. The shares shown include
      shares issuable pursuant to options held by the named person that may be
      exercised within 60 days of June 30, 2003.

(2)   Percentages of ownership are based upon 29,857,073 shares of Common Stock
      issued and outstanding as of June 30, 2003. Shares of Common Stock that
      may be acquired pursuant to options that are exercisable within 60 days of
      June 30, 2003 are deemed outstanding for computing the percentage
      ownership of the person holding such options, but are not deemed
      outstanding for the percentage ownership of any other person.

(3)   Includes 19,000 shares held by a trust for the benefit of Dr. Schimmel's
      sister, of which Dr. Schimmel is the trustee. Includes 40,000 shares
      issuable pursuant to stock options which are exercisable within 60 days of
      June 30, 2003.

(4)   Includes 60,000 shares held by Dr. Rich's spouse. Includes 40,000 shares
      issuable pursuant to stock options which are exercisable within 60 days of
      June 30, 2003.

(5)   Includes 64,000 shares issuable pursuant to stock options which are
      exercisable within 60 days of June 30, 2003.

(6)   Includes 54,000 shares issuable pursuant to stock options which are
      exercisable within 60 days of June 30, 2003.

(7)   Includes 610,000 shares issuable pursuant to stock options which are
      exercisable within 60 days of June 30, 2003.

(8)   Includes 160,000 shares issuable pursuant to stock options which are
      exercisable within 60 days of June 30, 2003.

(9)   Includes 122,000 shares issuable pursuant to stock options which are
      exercisable within 60 days of June 30, 2003.

(10)  Includes 968,000 shares issuable pursuant to stock options which are
      exercisable within 60 days of June 30, 2003.

                        SUMMARY OF EXECUTIVE COMPENSATION

                           Summary Compensation Table

      The table below shows compensation information with respect to services
rendered to Repligen in all capacities during the fiscal years ended March 31,
2003, 2002 and 2001 for the Chief Executive Officer and each of Repligen's other
most highly compensated executive officers who earned more than $100,000 in
salary and bonus in fiscal 2003 and were serving as executive officers as of
March 31, 2003 (collectively, the "Named Executive Officers").


                                     - 7 -



                                                                                                     Long-Term
                                                                                                   Compensation(2)
                                                                                                   ---------------
                                              Fiscal            Annual Compensation (1)           Shares Underlying
                                                                -----------------------
Name and Principal Position                    Year         Salary       Bonus       Other(3)         Options (#)
---------------------------                  --------     ----------   ---------    ----------     --------------
                                                                                        
Walter C. Herlihy, Ph.D......................  2003        $265,000     $65,000         $800           65,000
President and Chief Executive Officer          2002         242,000      50,000         $800           50,000
                                               2001         220,000      40,000           --           50,000

James R. Rusche, Ph.D. ......................  2003        $192,000     $25,000         $800           25,000
Senior Vice President, Research and            2002         172,000      25,000         $800           25,000
Development                                    2001         150,000      25,000           --           25,000

Daniel P. Witt, Ph.D.........................  2003        $162,000     $20,000         $800           20,000
Vice President, Business Development           2002         152,000      20,000         $800           20,000
                                               2001         142,000      10,000           --               --


--------------
(1) In accordance with the rules of the Securities and Exchange Commission,
other compensation in the form of perquisites and other personal benefits has
been omitted in those instances where the aggregate amount of such perquisites
and other personal benefits was less than the lower of $50,000 or 10% of the
total annual salary and bonus for the Named Executive Officer for such year.

(2) Represents stock options granted during the fiscal years ended March 31,
2003, 2002 or 2001. Repligen did not grant any restricted stock awards or stock
appreciation rights or make any long-term incentive plan payouts during the
fiscal years ended March 31, 2003, 2002 or 2001.

(3) Represents the match, paid by Repligen on behalf of such individual into the
Repligen Corporation 401(k) Savings Plan, of 50% of the first 5% for 2003 and
20% of the first 5% for 2002, of salary and bonus contributed by such individual
subject to a maximum of $800 in both years.


Option Grants in Last Fiscal Year

The following table shows information regarding stock options granted to the
Named Executive Officers during the fiscal year ending March 31, 2003.


                       OPTIONS GRANTED IN LAST FISCAL YEAR



                                 Number of        Percent of                                            Potential
                                 Securities     Total Options                                  Realizable Value at Assumed
                                 Underlying       Granted to      Exercise                     Annual Rates of Stock Price
                                  Options        Employees in      Price       Expiration           Appreciation For
Name                            Granted (#)      Fiscal Year      ($/Share)       Date                Option Term (1)
----                            -----------      -----------      ---------      ------     ------------------------------
                                                                                                  5%               10%
                                                                                            -------------     ------------

                                                                                            
Walter Herlihy, Ph.D. ........    50,000 (2)          18%           $3.24      4/11/2012     $   101,881      $   258,186
James R. Rusche, Ph.D. .......    25,000 (2)           9%           $3.24      4/11/2012     $    50,940      $   129,093
Daniel P. Witt, Ph.D. ........    20,000 (2)           7%           $3.24      4/11/2012     $    40,752      $   103,275


--------------
(1) These amounts represent hypothetical gains that could be achieved from the
exercise of respective options and the subsequent sale of the Common Stock
underlying such options if the options were exercised immediately prior to the
end of the option term. These gains are based on assumed rates of stock price
appreciation of 5% and 10% compounded annually from the date the respective
options were granted to their expiration dates. The gains shown are net of the
option exercise price, but do not include deductions for taxes or other expenses
associated with the exercise of the options or sale of the underlying shares.


                                     - 8 -


The actual gains, if any, on the stock option exercises will depend on the
future performance of the Common Stock, the optionholder's continued employment
through the option period, the date on which the options are exercised, and the
date on which the underlying shares of Common Stock are sold. These rates of
appreciation are mandated by the rules of the Securities and Exchange Commission
and do not represent Repligen's estimate or projection of the future Common
Stock price.

(2) The option holder may exercise the option to purchase 20% of these shares of
Common Stock on April 11, 2003 and an additional 20% per year on the next four
anniversaries thereof.

Option Exercises and Fiscal Year-End Values

The following table provides information regarding stock option exercises by the
Named Executive Officers and the number and value of the Named Executive
Officers' unexercised options at March 31, 2003.

              Aggregated Option Exercises In Last Fiscal Year And
                         Fiscal Year-End Option Values



                             Shares                         Number of Securities
                            Acquired                       Underlying Unexercised       Value of Unexercised In-the-
                           on Exercise  Value Realized   Options at Fiscal Year-End             Money Options
Name                           (1)            ($)                    (2)                   at Fiscal Year-End (3)
----                       -----------  --------------  ----------------------------   -----------------------------
                                                        Exercisable    Unexercisable   Exercisable     Unexercisable
                                                        -----------    -------------   ------------    -------------
                                                                                        
Walter C. Herlihy.......       --             --          580,000         120,000       $1,826,200        $151,900
James R. Rusche.........       --             --          140,000          70,000       $  405,370        $ 95,150
Daniel P. Witt..........       --             --          109,000          46,000       $  338,080        $ 79,960


(1) None of the Named Executive Officers exercised any stock options during the
fiscal year ended March 31, 2003.

(2) Represents the aggregate number of stock options held as of March 31, 2003
which can and cannot be exercised pursuant to the terms and provisions of the
applicable stock option agreements and the 2001 Repligen Corporation Stock
Option Plan (the "Plan").

(3) The dollar values have been calculated by determining the difference between
the fair market value of the securities underlying the options and the exercise
price of the options. The fair market value of in-the-money options was
calculated on the basis of the closing price per share for Common Stock on the
Nasdaq National Market of $4.67 on March 31, 2003. Of the 1,065,000 options
outstanding, 829,000 of these options were in the money as of March 31, 2003.

Equity Compensation Plan Information

      The following table provides information about the Common Stock that may
be issued upon the exercise of options, warrants and rights under all of the
Company's existing equity compensation plans as of March 31, 2003, including the
Plan.



                                                                                                 Number of securities
                                                                                                remaining available for
                                                                                                 future issuance under
                                          Number of securities to       Weighted-average          equity compensation
                                          be issued upon exercise      exercise price of           plans (excluding
                                          of outstanding options,     outstanding options,      securities reflected in
             Plan category                  warrants and rights       warrants and rights            columns (a))
             -------------                -----------------------     -------------------       -----------------------
                                                    (a)                       (b)                         (c)
                                                                                              
Equity compensation plans approved by
security holders (1).....................        1,940,050                   $2.55                     1,300,769

Equity compensation not approved by
security holders (2).....................          404,946                   $5.09                            --

Total ...................................        2,344,996                   $2.99                     1,300,769



                                     - 9 -


(1) Consists of the 2001 Repligen Corporation Stock Option Plan and the 1992
Repligen Corporation Stock Option Plan.

(2) On July 24, 2000, Repligen issued to a third party a warrant to purchase
50,000 shares of Common Stock at $7.125 per share exercisable through July 2003
in partial consideration for a licensing agreement entered into with such third
party. As of March 31, 2003 the warrant was still outstanding and no warrants
had been exercised.

On March 9, 2000, Repligen issued to Paramount Capital, Inc. ("Paramount")
warrants to purchase up to 129,946 shares of Common Stock at $9.49 per share,
exercisable through March 2005 in connection with services provided by
Paramount. As of March 31, 2003, this warrant remains outstanding.

In connection with a financial advisory agreement in May 2000, Repligen issued
warrants to purchase an aggregate of 100,000 shares of Common Stock. Each
warrant is exercisable at $2.75 per share at any time prior to July 15, 2004. As
of March 31, 2003, these warrants remain outstanding.

Also, pursuant to a patent purchase agreement executed in 1999 Repligen issued a
warrant to purchase 350,000 shares of common stock with an exercise price of
$1.59 per share which expires in March 2004. As of March 31, 2003, 225,000 of
the shares of Common Stock underlying the warrant have been issued and 125,000
shares remain eligible to be exercised.


                            Compensation of Directors

      Drs. Schimmel and Rich, the Co-Chairmen of the Board of Directors, are
compensated pursuant to consulting agreements described below and receive no
separate compensation for attendance at meetings or otherwise as directors.

      Under the terms of the Plan as currently in effect, each non-employee
director, beginning on September 14, 2000, is granted an option to purchase
10,000 shares of Common Stock at an option price equal to the fair market value
of the Common Stock on the date of grant, determined in accordance with the
terms of the Plan (the "Annual Board Options"). These options vest in full on
the first anniversary of the date of the grant, provided such person is still a
director on such anniversary. Additionally, each newly-elected, non-employee
director who joins the Board is entitled to receive a an option to purchase
24,000 shares of Common Stock on the date he or she joins the Board (an "Initial
Board Option" and together with the Annual Board Options, the "Board Options").
These Initial Board Options vest equally over a three-year period from the date
of grant. Board Options have a term of ten years, subject to early termination
in the event of death, removal or resignation from the Board. No director is
entitled to receive Board Options covering more than an aggregate of 100,000
shares. If the stockholders approve the amendment to the Plan described in
Proposal 5 herein, beginning in September 2003, each non-employee director will
receive an option to purchase 15,000 shares of Common Stock to vest in full on
the first anniversary of the date of grant, provided that such person is still a
director on such anniversary. No director would be entitled to receive Board
Options covering more than an aggregate of 150,000 shares of Common Stock,
excluding expired unexercised options.

      Mr. Hennessey and Mr. Miller receive $1,000 plus expenses for each board
meeting they attend. Starting in September 2003, each non-employee director
(other than Drs. Rich and Schimmel) will receive $1,500 plus expenses for each
board meeting they attend. In addition, also beginning in September 2003, the
Chairman of the Audit Committee will receive $1,500 plus expenses for each
meeting attended and each other Audit Committee member will receive $1,000 plus
expenses for each meeting in which they participate (other than Dr. Rich).

      Repligen paid Drs. Schimmel and Rich $49,200 and $43,200, respectively,
during the fiscal year ended March 31, 2003 pursuant to consulting agreements,
which have similar terms. These agreements are automatically extended for
successive one-year terms unless terminated by either party at least 90 days
prior to the next anniversary date. Dr. Schimmel's agreement continues until
September 30, 2003 and Dr. Rich's agreement continues until October 31, 2003.
Drs. Schimmel and Rich have advised Repligen that they have no present intention
of terminating their agreements.


                                     - 10 -


Executive Employment Agreements

      On March 14, 1996, Repligen entered into a letter of agreement with Drs.
Herlihy, Rusche, and Witt in connection with Repligen's acquisition and merger
with Glycan Pharmaceuticals, Inc. (the "Herlihy Agreement," the "Rusche
Agreement," and the "Witt Agreement," respectively). Under the terms of the
Herlihy Agreement, Dr. Herlihy is entitled to a minimum salary of $160,000 per
annum, subject to periodic increases at the discretion of the Board of
Directors. Additionally, Dr. Herlihy is eligible for participation in all of
Repligen's welfare, profit sharing, retirement and savings plans on the same
basis as other employees of Repligen. Dr. Herlihy received a stock option to
purchase 100,000 shares of the Common Stock at $1.25 per share, vesting at 20%
per annum over five years pursuant to the Herlihy Agreement. Dr. Herlihy's
employment may be terminated, with or without cause, by either party upon 30
days prior written notice. In such event, Dr. Herlihy would be entitled to
continue receiving his salary for a period of eight months or until he finds
other employment, whichever occurs first.

      Under the terms of the Rusche Agreement, Dr. Rusche is entitled to a
minimum salary of $115,000 per annum, subject to periodic increases at the
discretion of the Board of Directors. Additionally, Dr. Rusche is eligible for
participation in all of Repligen's welfare, profit sharing, retirement and
savings plans on the same basis as other employees of Repligen. Dr. Rusche
received a stock option to purchase 60,000 shares of the Common Stock at $1.25
per share, vesting at 20% per annum over five years pursuant to the Rusche
Agreement. Dr. Rusche's employment may be terminated, with or without cause, by
either party upon 30 days prior written notice. In such event, Dr. Rusche would
be entitled to continue receiving his salary for a period of six months or until
he finds other employment, whichever occurs first.

      Under the terms of the Witt Agreement, Dr. Witt is entitled to a minimum
salary of $115,000 per annum, subject to periodic increases at the discretion of
the Board of Directors. Additionally, Dr. Witt is eligible for participation in
all of Repligen's welfare, profit sharing, retirement and savings plans on the
same basis as other employees of Repligen. Dr. Witt received a stock option to
purchase 60,000 shares of the Common Stock at $1.25 per share, vesting at 20%
per annum over five years pursuant to the Witt Agreement. Dr. Witt's employment
may be terminated, with or without cause, by either party upon 30 days prior
written notice. In such event, Dr. Witt would be entitled to continue receiving
his salary for a period of six months or until he finds other employment,
whichever occurs first.

Compensation Committee Interlocks and Insider Participation

      The Compensation Committee currently consists of Dr. Schimmel and Mr.
Miller. No member of the Compensation Committee is a current or former employee
of Repligen. There are no Compensation Committee interlocks between Repligen and
any other entities involving any of the executive officers or directors of such
entities. No interlocking relationship exists between any member of our Board of
Directors or our Compensation Committee and any member of the Board of Directors
or compensation committee of any other company and no such interlocking
relationship has existed in the past.

                          STOCK PRICE PERFORMANCE GRAPH

      The following graph compares the yearly percentage change in the
cumulative total stockholder return (change in stock price plus reinvested
dividends) on Repligen's Common Stock with the cumulative total return for the
Nasdaq Stock Market Index (U.S.) (the "Nasdaq Composite Index") and the Nasdaq
Pharmaceutical Stock Index (the "Nasdaq Pharmaceutical Index"). The comparisons
in the graph are required by the Securities and Exchange Commission and are not
intended to forecast or be indicative of possible future performance of
Repligen's Common Stock.


                                     - 11 -


                         NASDAQ                NASDAQ
                         Stock             Pharmaceutical          RGEN Closing
                      Market Index
        YEAR             (U.S.)             Stock Index            Stock Price
        1998              100                   100                    100
        1999              135                   127                    257
        2000              251                   267                    808
        2001              101                   201                    242
        2002              101                   207                    315
        2003               74                   162                    392

   [THE ABOVE TABLE WAS REPRESENTED BY A LINE GRAPH IN THE PRINTED MATERIAL.]

Assumes $100 invested on March 31, 1998 in each of Repligen Corporation's Common
Stock, the securities comprising the Nasdaq Composite Index and the securities
comprising the Nasdaq Pharmaceutical Index.


                  COMPENSATION COMMITTEE REPORT TO STOCKHOLDERS

      The Compensation Committee, which meets on a periodic basis, is comprised
of two non-employee members of the Board of Directors. The Compensation
Committee formulates and administers Repligen's compensation policies for the
President and Chief Executive Officer and all vice presidents of Repligen. The
Compensation Committee is also responsible for determining to whom and under
what terms stock options should be granted (other than options which are
automatically granted to members of the Board of Directors) under the Plan.

Compensation Philosophy

      In designing its compensation programs, Repligen takes into account a
number of considerations, some relevant to companies in general and some
relevant primarily to biotechnology and other research and development intensive
companies. The ultimate goal of Repligen's compensation program is to motivate
each employee to enhance stockholder value, to provide a fair reward for this
effort, and to stimulate each employee's professional and personal growth. In
addition, Repligen's compensation program attempts to achieve the following:

      o     Provide compensation which is consistent with Repligen's annual and
            long-term objectives and achievements;

      o     Promotion and reward of individual initiative, effort and
            accomplishment; and

      o     Establishment of a competitive total compensation package that
            enables Repligen to attract and retain qualified and motivated
            personnel.

Performance Criteria

      Since Repligen is still in the process of developing its proprietary
products and because of the highly volatile nature of biotechnology stocks in
general, it is not appropriate to use the traditional performance standards,
such as profit levels and stock performance, to measure the success of Repligen
and an individual's contribution to that success.

      Accordingly, the compensation of executive officers is based, for the most
part, on the achievement of certain goals by Repligen as a whole and the
individual (and his or her business unit) concerned. The Compensation Committee


                                     - 12 -


therefore examines three specific areas in formulating the compensation packages
of its three most senior executives. Criteria and specific goals within each
category are as follows:

      Company Performance:

      o     The extent to which key research, clinical, product manufacturing,
            product sales and financial objectives of Repligen have been met
            during the preceding fiscal year;

      o     The development, acquisition and licensing of key technology; and

      o     The achievement by Repligen of certain milestones, whether specified
            in agreements with third party collaborators or determined
            internally.

      Executive Performance:

      o     An executive's involvement in and responsibility for the development
            and implementation of strategic planning and the attainment of
            strategic objectives of Repligen;

      o     The participation by an executive in the relationship between
            Repligen and the investment community;

      o     The involvement of an executive in personnel recruitment, retention
            and morale; and

      o     The responsibility of the executive in working within budgets,
            controlling costs and other aspects of expense management.

      Other Factors:

      o     The necessity of being competitive with companies in the
            pharmaceutical and biotechnology industries, taking into account
            relative company size, stage of development, performance and
            geographic location as well as individual responsibilities and
            performance.

Mix of Compensation

      Repligen's executive compensation has four principal components:

      o     base salary;

      o     annual cash bonuses;

      o     incentive and/or non-qualified stock options; and

      o     miscellaneous benefits.

      In each case, the Committee regularly compares the individual elements
comprising Repligen's executives' mix of compensation to that of a similar group
of other biotechnology companies.

      The comparison group is based on a multi-tiered classification of
representative companies within the biotechnology industry according to numerous
characteristics, including but not limited to company size, the number of
proprietary products, stage of development of Repligen's products and total
revenues. The tiered classification of biotechnology companies is reviewed
annually and, if appropriate, revised as members of such tiers change from year
to year.

      After completing a review of the comparison group's compensation policies,
the Committee determines competitive compensation levels for each executive
position.

      Levels of base salary are reviewed on an annual basis by the Committee.
Base salary may be altered in line with changes in compensation amongst the
companies included in the Committee's comparison group and further adjusted if
the committee determines that an executive's contribution to Repligen has
increased or decreased.


                                     - 13 -


      Annual cash bonuses are voted in April and calculated as a percentage of
an executive's base salary as determined by the criteria set forth above. Stock
options are also awarded from time to time based upon the same criteria and are
intended both to retain and reward the executive and to provide further
incentive for him or her to continue contributing to the long-term success of
Repligen.

Respectfully submitted by the Compensation Committee,

G. William Miller
Paul Schimmel, Ph.D.

      The report of the Compensation Committee shall not be deemed to be
"soliciting material," shall not be deemed filed with the Securities and
Exchange Commission, shall not be deemed incorporated by reference by any
general statement incorporating by reference this proxy statement into any
filing under the Securities Act of 1933 or under the Securities Exchange Act of
1934, except to the extent that Repligen specifically incorporates this
information by reference, and shall not otherwise be deemed filed under such
Acts.

                          REPORT OF THE AUDIT COMMITTEE

      The Audit Committee for the last fiscal year consisted of Dr. Rich,
Committee Chairman, Mr. Hennessey and Mr. Miller. Each of the current members of
the Audit Committee is independent (as defined in the current NASDAQ's listing
standards). Dr. Rich would not be independent under the newly proposed NASDAQ
listing standards, and would not be able to continue as an audit committee
member upon the effectiveness of such standards. If Proposals 2 and 3 are
approved by the stockholders, the intent of the Board is that Mr. Ryan will
serve on the Audit Committee upon his election to the Board of Directors, at
which time the Audit Committee will elect a new Chairman. Upon the election of
Mr. Ryan, or another qualified individual, to the Audit Committee, Dr. Rich
intends to resign as a member of the Audit Committee. The Board has determined
that none of the members of the Audit Committee has a relationship to Repligen
that may interfere with his independence from Repligen and its management.

      The primary function of the Audit Committee is to assist the Board of
Directors in fulfilling its oversight responsibilities by reviewing financial
reports and other financial information provided by the Company to any
governmental body or the public, the Company's systems of internal controls
regarding finance, accounting, legal compliance and ethics that management and
the Board have established, and the Company's auditing, accounting and financial
processes generally. The Audit Committee annually recommends to the Board of
Directors the appointment of a firm of independent auditors to audit the
financial statements of the Company and meets with such personnel of the Company
to review the scope and the results of the annual audit, the amount of audit
fees, the Company's internal accounting controls, the Company's financial
statements contained in the Company's Annual Report to Stockholders and other
related matters. The Audit Committee's Charter, which was adopted by the
Company's Board of Directors, contains a more detailed description of the
functions of the Audit Committee.

      The Audit Committee has reviewed and discussed with management the
financial statements for fiscal year 2003 audited by Ernst & Young LLP, the
Company's independent auditors. The Audit Committee has discussed with Ernst &
Young LLP various matters related to the financial statements, including those
matters required to be discussed by SAS 61 (Codification of Statements on
Auditing Standards, AU 380). The Audit Committee has also received the written
disclosures and the letter from Ernst & Young LLP required by Independence
Standards Board Standard No. 1 (Independence Standards Board Standard No. 1,
Independence Discussions with Audit Committees), and has discussed with Ernst &
Young LLP its independence. Based upon such review and discussions, the Audit
Committee recommended to the Board of Directors that the audited financial
statements be included in the Company's Annual Report on Form 10-K for the
fiscal year ending March 31, 2003 for filing with the Securities and Exchange
Commission.

AUDIT COMMITTEE

Dr. Alex Rich, Chairman
Robert Hennessey
G. William Miller


                                     - 14 -


      The report of the Audit Committee shall not be deemed to be "soliciting
material," shall not be deemed filed with the Securities and Exchange
Commission, shall not be deemed incorporated by reference by any general
statement incorporating by reference this proxy statement into any filing under
the Securities Act of 1933 or under the Securities Exchange Act of 1934, except
to the extent that Repligen specifically incorporates this information by
reference, and shall not otherwise be deemed filed under such Acts.

Relationship with Independent Auditors

      Effective June 12, 2002, as recommended by the Audit Committee, the Board
of Directors of Repligen dismissed Arthur Andersen LLP ("Arthur Andersen") as
its independent certifying accountants and engaged Ernst & Young LLP to serve as
its independent certifying accountants for the fiscal year ending March 31,
2003. The appointment of Ernst & Young LLP was ratified by the stockholders of
the Company at the Annual Meeting of Stockholders on September 12, 2002.

      Arthur Andersen's audit reports on Repligen's financial statements for
each of the two fiscal years ended March 31, 2002 and 2001 did not contain an
adverse opinion or disclaimer of opinion nor were they qualified or modified as
to any uncertainty, audit scope or accounting principles. In connection with the
audits for the periods ending March 31, 2002 and 2001 and the subsequent interim
period preceding the dismissal of Arthur Andersen, there were no disagreements
with Arthur Andersen on any matter of accounting principles or practices,
financial statement disclosure or auditing scope or procedure, which, if not
resolved to the satisfaction of Arthur Andersen, would have caused them to refer
to such disagreement in connection with their report. None of the reportable
events as defined in Item 304(a)(1)(v) of Regulation S-K occurred within the
fiscal years of Repligen ended March 31, 2002 and 2001 or the interim period
through June 12, 2002.

      During Repligen's fiscal years ended March 31, 2002 and 2001 and the
interim period through June 12, 2002, Repligen did not consult Ernst & Young LLP
with respect to the application of accounting principles to a specified
transaction, either completed or proposed, or the type of audit opinion that
might be rendered on Repligen's financial statements.

      Ernst & Young LLP has been the independent audit firm that audits the
financial statements of the Company since June 12, 2002. In accordance with
standing policy, Ernst & Young LLP periodically changes the personnel who work
on the audit.

Audit Fees

      The aggregate fees billed by Ernst & Young LLP for professional services
rendered for the audit of Repligen's annual financial statements for the fiscal
year ended March 31, 2003 and for the review of the financial statements
included in Repligen's Forms 10-Q for the fiscal year ended March 31, 2003 were
$51,500.

Financial Information Systems Design and Implementation Fees

      No fees were billed by Ernst & Young LLP for financial information systems
design and implementation professional services for the fiscal year ended March
31, 2003.

All Other Fees

      The aggregate fees billed by Ernst & Young LLP for services other than
those described above for the fiscal year ended March 31, 2003 were $11,500.

      Repligen's Audit Committee has determined that the provision of the
services provided by Ernst & Young LLP as set forth herein are compatible with
maintaining Ernst & Young LLP's independence.


                                     - 15 -


                                   PROPOSAL 2
             INCREASE IN SIZE OF BOARD OF DIRECTORS TO EIGHT MEMBERS

      Currently, Repligen's by-laws require that the number of directors
constituting the Board be fixed by a resolution of the stockholders. Repligen
currently has five (5) directors constituting its whole Board of Directors.

      Repligen's Board of Directors has approved and recommends that the
stockholders approve an increase in the number of Directors to eight (8)
members. Repligen's Board is actively searching for high-quality individuals to
strengthen and improve the Board. Specifically, in order to satisfy regulatory
requirements, the Nominating Committee has been searching for an "audit
committee financial expert" to replace Dr. Rich as Chairman of the Audit
Committee. As a result of the search, the Nominating Committee has nominated Mr.
Ryan for election to the Board of Directors if this Proposal 2 is approved by
the stockholders, with the intent that Mr. Ryan will serve on the Audit
Committee. Dr. Rich has informed us that it is his intention to resign as
Chairman of the Audit Committee as soon as a candidate qualified to serve on the
Audit Committee is duly elected to the Board of Directors. If this proposal is
not passed, we may not be able to comply with our regulatory requirements.

      The Board of Directors recommends a vote FOR the increase in the size of
the Board of Directors to eight members.


                                   PROPOSAL 3
            ELECTION OF THOMAS F. RYAN, JR. TO THE BOARD OF DIRECTORS

      If Proposal 2 is approved, there will be three vacancies on the Board of
Directors. Pursuant to the current Bylaws, a resolution of the stockholders is
required to fill such vacancy. Information regarding Mr. Ryan has been provided
in the "Occupation of Directors and Executive Officers," "Biographical
Information" and "Stock Ownership of Directors and Officers."

      Repligen's Nominating Committee has nominated Mr. Ryan and the Board of
Directors recommends that the stockholders elect Mr. Ryan to the Board of
Directors to fill the vacancy created by the approval of Proposal 2. As stated
above, it is the intent of the Board that Mr. Ryan will, if elected, serve on
the Audit Committee as an "audit committee financial expert" and his service on
the Audit Committee will enable us to meet certain new regulatory requirements
pursuant to the Sarbanes-Oxley Act. If Mr. Ryan is not elected to the Board, we
may not be able to comply with our regulatory requirements.

      The Board of Directors recommends a vote FOR the election of Mr. Ryan to
the Board of Directors.

                                   PROPOSAL 4
  AMENDMENT TO BY-LAWS TO ALLOW BOARD TO INCREASE SIZE OF BOARD OF DIRECTORS
         AND TO ALLOW BOARD TO FILL VACANCIES ON THE BOARD OF DIRECTORS

      The Board of Directors recommends to the stockholders that the by-laws be
amended (the "By-law Amendment") to allow for (i) the size of the Board of
Directors of the Company to be fixed by a resolution of the Board of Directors,
and (ii) vacancies on the Board of Directors to be filled by resolution of the
Board of Directors. Currently, the size of the Board of Directors may only be
changed by, and any vacancies on the Board of Directors may only be filled by, a
resolution of the stockholders.

      The text of the by-laws, as currently in effect, as well as the text of
the amendment approved by the Board, is attached to this proxy statement as
Appendix A. The following summary should be read together with the full text of
the by-laws and the amendment thereto.

      The Board of Directors has approved, and recommends that the stockholders
approve the By-law Amendment that will allow the Company to set the number of
directors constituting the whole Board and that any vacancy in the Board of
Directors, however occurring, may be filled by resolution of the Board. A
director elected to fill a vacancy shall hold office until the next annual
meeting of stockholders and until his or her successor is elected and qualified
or until his or her earlier death, resignation or removal.


                                     - 16 -


      The purpose of the By-law Amendment is to increase the Company's ability
to seat high-quality individuals as directors of the Company. The Board of
Directors has determined that increasing the number of authorized directors is
in the best interest of the Company and its stockholders. By allowing the Board
of Directors the ability to appoint additional directors until the next annual
meeting, the Company can seat such individuals as they are found and not require
their appointment to wait until the next annual meeting. For example, we will
likely be required to have at least three independent directors serve on our
Audit Committee pursuant to Sarbanes-Oxley related requirements. Currently, we
would not meet the proposed requirements. We are actively searching for new
members to add to the Board who would allow us to meet these requirements. If
Proposal 2 is not approved by the stockholders, but the By-Law Amendment is
approved, it is the intent of the Board to increase the size of the Board to
eight (8) members and to appoint Mr. Ryan to fill one of the vacancies created
by the increase in the size of the Board.

      The Board of Directors recommends a vote FOR the approval of the By-Law
Amendment.

                                   PROPOSAL 5
              AMEND THE 2001 REPLIGEN CORPORATION STOCK OPTION PLAN
                            TO INCREASE BOARD OPTIONS

      The Plan was adopted by the Company's Board of Directors and approved by
the Company's stockholders at our September 2001 Annual Meeting of Stockholders.
The Board of Directors has approved and recommends to the stockholders that they
approve an amendment to increase the number of stock options automatically
granted each year to non-employee directors of the Company under the Plan as of
September 10, 2003.

      Under the terms of the Plan, as currently in effect, each non-employee
director of the Company is entitled to a grant of an option to purchase 24,000
shares of Common Stock (the "Initial Board Option") on the date such person
becomes a member of the Board of Directors. Such options vest equally on an
annual basis over a three-year period from the date of grant. In addition, each
of the Company's existing non-employee directors is granted an option each year
to purchase 10,000 shares of Common Stock (the "Annual Board Options," and
together with the Initial Board Option, the "Board Options") which vests in full
on the first anniversary of the date of the grant, provided such person is still
a director of the Company on such anniversary. The Plan presently provides for
an overall limitation on Board Options of 100,000 Board Options per eligible
director.

      The Board proposes to amend the Plan to provide for an annual grant to
each of its existing non-employee directors of an option to purchase 15,000
shares of Common Stock which will vest in full on the first anniversary of the
date of the grant, provided such person is still a director on such anniversary.
Accordingly, the Board also proposes to increase the overall limitation of
permissible Board Options to 150,000 Board Options per eligible director,
excluding expired, unexercised options.

      The Company believes that its future success is partly dependent on the
quality and continuity of its Board of Directors and desires to increase the
alignment of the interest of the members of the Board of Directors with the
Company. The Company relies on stock options as part of the compensation
packages necessary for the Company to attract and retain experienced directors.
The Board of Directors of the Company believes that the proposed increase in the
number of shares to be automatically granted to non-employee directors as Annual
Board Options will enable the Company to secure the attraction and retention of
superior individuals to serve as directors.

      The following table sets forth information regarding options which would
have been granted to each of Repligen's Named Executive Officers, all current
executive officers as a group, all current directors who are not executive
officers as a group and all employees other than executive officers as a group,
had the proposed amendment been in effect during the fiscal year ended March 31,
2003.

Name and Position                                      Number of Options Granted
-----------------                                      -------------------------
Walter C. Herlihy, Ph.D.............................            50,000
President and Chief Executive Officer

James R. Rusche, Ph.D...............................            25,000
Vice President, Research and Development

Daniel P. Witt, Ph.D................................            20,000
Vice President, Business Development

Executive Group (3 persons).........................            95,000

Non-Executive Director Group (4 persons)............            60,000

Non-Executive Officer Employee Group (30 persons)...           146,650


                                     - 17 -


      The Plan may not be amended to increase the maximum number of shares which
may be granted under the Plan (except under the anti-dilution provisions
contained therein) or to change the class of persons to whom options may be
granted without the affirmative vote of holders of Repligen's Common Stock.

Summary of the Plan As Currently in Effect

      The full text of the Plan (as proposed to be amended and restated) is set
forth as Appendix B to this proxy statement. The following summary of the
provisions of the Plan is qualified in its entirety by reference to the text of
the Plan.

Types of Options Authorized by the Plan

      The Plan permits the Company to grant both incentive stock options
("Incentive Stock Options") within the meaning of Section 422 of the Internal
Revenue Code of 1986, as amended (the "Code"), and other options which do not
qualify as Incentive Stock Options ("Non-Qualified Options"). Non-Qualified
Options will be granted in the sole discretion of the Committee referred to
below and certain other options (the "Board Options") are granted to eligible
non-employee members of the Board of Directors.

      The aggregate number of shares of Common Stock reserved for issuance under
the Plan is 3,254,619. As of June 30, 2003, there were 1,062,669 shares
available for grant under the Plan.

Administration

      To the extent that any issue arising under the Plan relates to Incentive
Stock Options and Non-Qualified Options, the members of a committee (the
"Committee") composed of two or more "outside directors" (as defined in
applicable resolutions under Section 162(m) of the Code) administers the Plan.
The members of the Committee are eligible to receive Board Options which are not
discretionary in nature. To the extent that any issue arising under the Plan
relates to the granting of Board Options, Repligen has designed the Plan to
operate automatically and without the need for administration; however, to the
extent that such administration is necessary the Committee will provide it.

Eligibility

      Incentive Stock Options. Repligen grants Incentive Stock Options only to
employees of the Company or any of its subsidiaries.

      Non-Qualified Options. Repligen grants Non-Qualified Options under the
Plan to directors and officers of the Company and full or part-time employees
employed on a salaried or commission basis by the Company or any of its
subsidiaries, as well as any individual performing services for the Company or
any subsidiary as an independent contractor.

      Board Options. Repligen grants Board Options only to members of the Board
of Directors of the Company, other than the current co-chairmen of the Board of
Directors, who are not employees of either the Company or any of its
subsidiaries.


                                     - 18 -


Grants Under the Plan

      Incentive Stock Options and Non-Qualified Options. Subject to the terms of
the Plan, the Committee has full authority to determine the individuals to whom,
and the time or times at which, Incentive Stock Options and Non-Qualified
Options are granted.

      Board Options. Each eligible director of the Company is entitled to
receive annually an option to purchase 10,000 shares of Common Stock and each
person who becomes a non-employee member of the Board of Directors shall receive
at the time such person first becomes a member of the Board of Directors an
option to purchase 24,000 shares of Common Stock. The Plan provides for an
overall limitation that no member of the Board of Directors shall receive Board
Options for in excess of 100,000 shares of Common Stock.

Option Prices

      Incentive Stock Options. The purchase price of Common Stock under each
Incentive Stock Option shall not be less than 100% of the fair market value of
the stock at the time of the granting of the option. For purposes of the Plan,
"fair market value" is equal to the NASDAQ National Market System closing price
(or the closing price on an exchange if the Common Stock is then traded on an
exchange) per share of Common Stock for the date of the grant of an option, or
such other amount as shall be determined from time to time by the Committee
pursuant to criteria which it may deem to be appropriate.

      Non-Qualified Options. The purchase price of Common Stock under
Non-Qualified Options shall be as determined in the sole discretion of the
Committee, although in no case shall the price per share be less than the par
value per share of Common Stock.

      Board Options. The purchase price of the Common Stock under each Board
Option shall be equal to the average NASDAQ National Market System closing price
per share of the Common Stock for the thirty (30) trading days immediately
preceding the date of grant of such Board Option.

Term

      If not presently exercised, all options granted under the Plan will expire
no later than ten years after the date of grant thereof.

Adjustments

      The Plan provides for adjustments in the number of shares reserved and in
option prices in the event of a stock dividend or stock split and for other
equitable adjustments in the event of recapitalization, merger or similar
occurrences.

Federal Income Tax Consequences

      Incentive Stock Options. The following general rules are applicable under
current federal income tax law to Incentive Stock Options under the Plan:

      1. In general, no taxable income results to the optionee upon the grant of
an Incentive Stock Option or upon the issuance of shares to him or her upon the
exercise of the Incentive Stock Option, and no tax deduction is allowed to the
Company upon either grant or exercise of an Incentive Stock Option.

      2. If shares acquired upon exercise of an Incentive Stock Option are not
disposed of within (i) two years following the date the option was granted or
(ii) one year following the date the shares are issued to the optionee pursuant
to the Incentive Stock Option exercise, the difference between the amount
realized on any subsequent disposition of the shares and the exercise price will
generally be treated as capital gain or loss to the optionee.

      3. If shares acquired upon exercise of an Incentive Stock Option are
disposed of before the expiration of one or both of the requisite holding
periods described above (a "Disqualifying Disposition"), then in most cases the
lesser of (i) any excess of the fair market value of the shares at the time of
exercise of the Incentive Stock Option over the exercise price or (ii) the


                                     - 19 -


actual gain on disposition will be treated as compensation to the optionee and
will be taxed as ordinary income in the year of such disposition.

      4. In any year that an optionee recognizes compensation income on a
Disqualifying Disposition of stock acquired by exercising an Incentive Stock
Option, the Company generally should be entitled to a corresponding deduction
for income tax purposes.

      5. Any excess of the amount realized by the optionee as the result of a
Disqualifying Disposition over the sum of (i) the exercise price and (ii) the
amount of ordinary income recognized under the above rules will be treated as
capital gain.

      6. Capital gain or loss recognized on a disposition of shares will be
long-term capital gain or loss if the optionee's holding period for the shares
exceeds one year.

      7. An optionee may be entitled to exercise an Incentive Stock Option by
delivering shares of the Company's Common Stock to the Company in payment of the
exercise price, if the optionee's Incentive Stock Option agreement so provides.
If an optionee exercises an Incentive Stock Option in such fashion, special
rules will apply.

      8. The general tax consequences above will not apply to an optionee who is
subject to "alternative minimum tax" under the Code. It is possible that the
exercise of an ISO would cause an employee to become subject to alternative
minimum tax. In general, the amount by which the value of the Common Stock
received upon exercise of the ISO exceeds the exercise price is included in the
optionee's alternative minimum taxable income.

      Non-Qualified Options and Board Options. The following general rules are
applicable under current federal income tax law to Non-Qualified Options under
the Plan:

      1. The optionee generally does not realize any taxable income upon the
grant of a Non-Qualified Option, and the Company is not allowed a business
expense deduction by reason of such grant.

      2. The optionee generally will recognize ordinary compensation income at
the time of exercise of a Non-Qualified Option in an amount equal to the excess,
if any, of the fair market value of the shares on the date of exercise over the
exercise price. The Company may be required to withhold income tax on this
amount.

      3. When the optionee sells the shares, he or she generally will recognize
a capital gain or loss in an amount equal to the difference between the amount
realized upon the sale of the shares and his or her basis in the shares
(generally, the exercise price plus the amount taxed to the optionee as
compensation income). If the optionee's holding period for the shares exceeds
one year, such gain or loss will be a long-term capital gain or loss.

      4. The Company generally should be entitled to a tax deduction when
compensation income is recognized by the optionee.

      5. An optionee may be entitled to exercise a Non-Qualified Option by
delivering shares of the Company's Common Stock to the Company in payment of the
exercise price. If an optionee exercises a Non-Qualified Option in such fashion,
special rules will apply.

      The Board of Directors recommends a vote FOR the approval of the proposal
to amend the 2001 Repligen Corporation Stock Option Plan to increase the number
of Board Options that the Company will automatically grant per year and the
aggregate number of Board Options that the Company will grant to its
non-employee directors under the Plan.

                                   PROPOSAL 6
        AMEND AND RESTATE 2001 REPLIGEN CORPORATION STOCK OPTION PLAN TO
                            INCLUDE RESTRICTED STOCK

      The Plan was adopted and approved by the Company's stockholders at our
September 2001 Annual Meeting of Stockholders. Since adoption, the only awards
eligible to be granted under the Plan have been stock options. In the opinion of


                                     - 20 -


the Board of Directors, the Company's future success depends, in large part,
upon our ability to maintain a competitive position in attracting, retaining and
motivating key personnel. To further this end, the Board of Directors has
approved and recommended amending and restating the Plan to include awards of
restricted stock. This proposal does not increase or otherwise affect the total
number of shares authorized for issuance under the Plan. To date, no awards of
restricted stock have been granted under the Plan. The sole purpose of this
proposal is to allow the Company flexibility to grant awards of restricted stock
under the Plan and accordingly the Plan (as amended and restated) provides the
Company with greater flexibility to reward officers, directors and employees of,
and consultants to, the Company for their past performance and to provide an
incentive to such persons to remain with the Company and for future performance.
Recent developments in employee compensation have favored the grant of
restricted stock rather than stock options. The Plan, as proposed to be amended
and restated, is attached as Appendix B to this Proxy Statement and is
incorporated herein by reference.

      The Company's management relies on awards under the Plan as an essential
part of the compensation packages necessary for the Company to attract and
retain experienced officers, directors and employees. The Board of Directors
believes that the present limitation on the type of awards eligible to be
granted under the Plan may not be adequate to attract, motivate and retain key
personnel given the current volatility in the equity markets, and that the
proposal to include awards of restricted stock under the Plan is essential to
permit the Company's Board of Directors to continue to provide long-term,
equity-based incentives to present and future key personnel.

Summary of Restricted Stock Awards under the Plan

      The following summary of the Restricted Stock Awards under the Plan is
qualified in its entirety by reference to the text of the Plan (as proposed to
be amended and restated) and as attached as Appendix B to this proxy statement.
A summary of the Plan (as currectly in affect) is set forth under Proposal 5.

Restricted Stock Awards Authorized by the Plan

      The Plan permits the Company to grant restricted stock awards ("Restricted
Stock Awards") in the Company's Common Stock.

      The aggregate number of shares of Common Stock reserved for issuance under
the Plan is 3,254,619. As of June 30, 2003, there were 1,062,669 shares
available for grant under the Plan.

Administration

      To the extent that any issue arising under the Plan relates to Restricted
Stock Awards, the Committee administers the Plan.

Eligibility

      Restricted Stock Awards may be granted to directors and officers of the
Company and full employees employed on a salaried or commission basis by the
Company or any of its subsidiaries, as well as any individual performing
services for the Company or any subsidiary as an independent contractor.

Grants Under the Plan

      Subject to the terms of the Plan, the Committee has full authority to
determine the individuals to whom, and the time or times at which Restricted
Stock Award should be and are granted.

Restrictions on Restricted Stock Awards

      A Restricted Stock Award under the Plan represents the right to receive a
specified number of shares of Common Stock subject to (a) certain forfeiture
provisions regarding such awards and/or (b) the satisfaction of any applicable
performance goals. The vesting restrictions and/or performance goals, if any,
will be set by the Committee at the time of the award.


                                     - 21 -


      In the event no performance goals are applicable to a Restricted Stock
Award, promptly after the forfeiture provisions applicable to such award, if
any, lapse, a stock certificate representing the appropriate number of shares of
Common Stock shall be issued to the recipient. In the event performance goals
are applicable to an award, promptly after the forfeiture provisions applicable
to such award, if any, lapse, the Committee shall determine whether the
applicable performance goals have been achieved. If the Committee certifies that
the applicable performance goals have been achieved, a stock certificate
representing the appropriate number of shares of Common Stock shall be issued to
the recipient. If the Committee determines that the applicable performance goals
have not been achieved, the award shall be forfeited. Unless otherwise
determined by the Committee on or after the date of grant, in the event of a
participant's termination of employment for any reason, any award held by such
participant which was subject to provisions of forfeiture, either because time
periods had not lapsed or goals were not achieved, shall be forfeited.

Award Prices

      The purchase price of Common Stock under each Restricted Stock Award shall
not be less than the par value of Common Stock.

Terms and Conditions

      The Committee shall determine the terms and conditions of any such
Restricted Stock Award, including the effect on a Restricted Stock Award of the
disability, death, retirement, authorized leave of absence or other change in
the employment or other status of the recipient.

Federal Income Tax Consequences of Restricted Stock Awards

      The following general rules are applicable under current federal income
tax law to Restricted Stock Awards under the Plan:

      1.    Persons receiving Common Stock pursuant to a Restricted Stock Award
            generally will recognize compensation income equal to the fair
            market value of the shares received, reduced by any purchase price
            paid.

      2.    The Company generally should be entitled to a corresponding
            deduction for federal income tax purposes when such person
            recognizes compensation income. When such Common Stock is sold, the
            seller generally will recognize capital gain or loss equal to the
            difference between the amount realized upon the sale and the
            seller's tax basis in the Common Stock (generally, the amount that
            the seller paid for such stock plus the amount taxed to the Seller
            as compensation income).

      3.    Special rules apply if the stock acquired pursuant to a Restricted
            Stock Award is subject to vesting, or is subject to certain
            restrictions on resale under federal securities laws applicable to
            directors, officers or 10% stockholders.

      The Board of Directors recommends a vote FOR the approval of the proposal
to amend and restate the Plan to allow for the grant of restricted stock awards
under the Plan.

                                   PROPOSAL 7
                RATIFICATION OF SELECTION OF INDEPENDENT AUDITORS

      The Audit Committee of the Board of Directors of Repligen Corporation
annually considers and recommends to the Board the selection of Repligen's
independent public accountants. On June 25, 2003, as recommended by the Audit
Committee, the Board of Directors of Repligen engaged Ernst & Young LLP to serve
as its independent certifying accountants for the fiscal year ending March 31,
2004, which engagement is being submitted to the stockholders for ratification
at the Annual Meeting. A member of the firm will be present at the Annual
Meeting with the opportunity to make a statement if so desired and will be
available to respond to appropriate questions. Stockholder ratification of the
Company's independent auditors is not required under Delaware law or under the
Company's Certificate of Incorporation or its by-laws. If stockholders do not
ratify the selection of Ernst & Young LLP as the Company's independent auditors


                                     - 22 -


for the current fiscal year ended March 31, 2004, the Company's Board of
Directors will evaluate what would be in the best interests of the Company and
its stockholders and consider whether to select new independent auditors for the
current fiscal year or whether to wait until the completion of the audit for the
current fiscal year before changing independent auditors.

      In connection with the audits for the period ending March 31, 2003, there
were no disagreements with Ernst & Young LLP on any matter of accounting
principles or practices, financial statement disclosure or auditing scope or
procedure, which, if not resolved to the satisfaction of Ernst & Young LLP,
would have caused them to refer to such disagreement in connection with their
report.


              SECTION 16 BENEFICIAL OWNERSHIP REPORTING COMPLIANCE

      Section 16(a) of the Securities Exchange Act of 1934 requires Repligen's
directors, officers, and holders of more than ten percent of Repligen's Common
Stock (collectively, "Reporting Persons"), to file with the Securities and
Exchange Commission ("SEC") initial reports of ownership and reports of changes
in ownership of Common Stock of Repligen. Such Reporting Persons are required by
SEC regulation to furnish Repligen with copies of all Section 16(a) reports they
file. Based on its review of the copies of such filings received by it with
respect to the fiscal year ended March 31, 2003, the Company believes that all
required persons complied with all Section 16(a) filing requirements except as
noted below. Drs. Rich, Schimmel and Messrs. Hennessey and Miller each had one
late filing to report a single transaction.

                             STOCKHOLDERS' PROPOSALS

      Repligen must receive any proposal by a stockholder of Repligen intended
to be presented at the 2004 Annual Meeting of Stockholders at its principal
executive office not later than February 27, 2004 for inclusion in Repligen's
proxy statement and form of proxy relating to that meeting. Any such proposal
must also comply with the other requirements of the proxy solicitation rules of
the SEC.

                                 OTHER BUSINESS

      Management does not know of any other matters to be brought before the
Meeting except those set forth in the notice thereof. If other business is
properly presented for consideration at the Meeting, it is intended that the
Proxies will be voted by the persons named therein in accordance with their
judgment on such matters.

      Even if you plan to attend the Meeting in person, please sign, date and
return the enclosed Proxy promptly. A postage-paid return-addressed envelope is
enclosed for your convenience. Your cooperation in giving this matter your
immediate attention and in returning your proxies will be appreciated.

                            EXPENSES AND SOLICITATION

      The cost of solicitation will be borne by Repligen, and in addition to
directly soliciting stockholders by mail, Repligen may request banks and brokers
to solicit their customers who have stock of Repligen registered in the name of
the nominee and, if so, will reimburse such banks and brokers for their
reasonable out-of-pocket costs. Solicitation by officers and employees of
Repligen may also be made of some stockholders in person or by mail or telephone
following the original solicitation. Repligen has retained MacKenzie Partners, a
proxy solicitation firm, to assist in the solicitation of proxies for a fee of
approximately $6,500 plus reimbursement of expenses.

                                  HOUSEHOLDING

      Our Annual Report, including audited financial statements for the fiscal
year ended March 31, 2003, is being mailed to you along with this Proxy
Statement. In order to reduce printing and postage costs, ADP Investor
Communication Services has undertaken an effort to deliver only one Annual
Report and one Proxy Statement to multiple stockholders sharing an address. This
delivery method, called "householding," is not being used, however, if ADP has
received contrary instructions from one or more of the stockholders sharing an
address. If your household has received only one Annual Report and one Proxy
Statement, Repligen Corporation will deliver promptly a separate copy of the
Annual Report and the Proxy Statement to any stockholder who sends a written
request to Repligen Corporation, 41 Seyon Street, Building 1, Waltham, MA,
02453, Attention: Secretary.


                                     - 23 -


                                                                      Appendix A

                                     BY-LAWS

                                       OF

                              REPLIGEN CORPORATION


                                    ARTICLE I

                                  STOCKHOLDERS


      SECTION 1. Place of Meetings. All meetings of stockholders shall be held
at such place within or without the State of Delaware as may be designated from
time to time by the Board of Directors or, if not so designated, at the
principal office of the corporation.

      SECTION 2. Annual Meeting. The annual meeting of stockholders of the
election of directors and the transaction of such other business as may properly
come before the meeting shall be held at 10 a.m. on the last Thursday in July of
each year or on such other date or at such hour as may be specified by
resolution of the Board of Directors. If the date of the annual meeting shall
fall upon a legal holiday at the place of the meeting, the meeting shall be held
at the same hour on the next succeeding business day. If the annual meeting is
not held on the date designated therefor, the directors shall cause the meeting
to be held as soon thereafter as convenient.

      SECTION 3. Special Meetings. Special meetings of the stockholders may be
called at any time by the President, the Chairman, or the Board of Directors, or
by the Secretary or any other officer upon the written request of one or more
stockholders holding of record at least a majority of the outstanding shares of
stock of the corporation entitled to vote at such meeting. Such written request
shall state the purpose or purposes of the proposed meeting. Business transacted
at any special meeting of stockholders shall be limited to matters relating to
the purpose or purposes stated in the notice of meeting.

      SECTION 4. Notice of Meetings. Except where some other notice is required
by law, written notice of each meeting of stockholders, stating the place, date
and hour thereof and the purposes for which the meeting is called, shall be
given by or under the direction of the Secretary, not less than ten nor more
than sixty days before the date fixed for such meeting, to each stockholder
entitled to vote at such meeting of record at the close of business on the day
fixed by the Board of Directors as a record date for the determination of the
stockholders entitled to vote at such meeting or, if not such date has been
fixed, of record at the close of business on the day before the day on which
notice is given. Notice shall be given personally to each stockholder or left at
his or her residence or usual place of business or mailed postage prepaid and
addressed to the stockholder at his or her address as it appears upon the
records of the corporation. In case of the death, absence, incapacity or refusal
of the Secretary, such notice may be given by a person designated either by a
Secretary or by the person or persons calling the meeting or by the Board of
Directors. A waiver of such notice in writing, signed by the person or persons
entitled to said notice, whether before or after the time stated therein, shall
be deemed equivalent to such notice. Attendance of a person at a meeting of
stockholders shall constitute a waiver of notice of such meeting, except when
the stockholder attends a meeting for the express purpose of objecting, at the
beginning of the meeting, to the transaction of any business because the meeting
is not lawfully called or convened. Neither the business to be transacted at,
nor the purpose of, any regular or special meeting of the stockholders need be
specified in any written waiver of notice. Notice of any meeting of the
stockholders shall be deemed to have been given to any person who may become a
stockholder of record after the mailing of such notice and prior to such
meeting. Except as required by statute, notice of any adjourned meeting of the
stockholders shall not be required.

      SECTION 5. Voting List. The officer who has charge of the stock ledger of
the corporation shall prepare and make, at least ten days before every meeting
of stockholders, a complete list of the stockholders, arranged in alphabetical
order, and showing the address of each stockholder and the number of shares
registered in the name of each stockholder. Such list shall be open to the
examination of any stockholder, for any purpose germane to the meeting, during


                                     - 1 -


ordinary business hours, for a period of at least ten days prior to the meeting,
either at a place within the city or other municipality or community where the
meeting is to be held, which place shall be specified in the notice of the
meeting, or if not so specified, at the place where the meeting is to be held.
The list shall also be produced and kept at the time and place of the meeting
during the whole time thereof, and may be inspected by an stockholder who is
present. The stock ledger shall be the only evidence as to who are the
stockholders entitled to examine the stock ledger, the list required by this
section or the books of the corporation, or to vote at any meeting of
stockholders.

      SECTION 6. Quorum of Stockholders. At any meeting of the stockholders, the
holders of a majority in interest of all stock issued and outstanding and
entitled to vote upon a question to be considered at the meeting, present in
person or represented by proxy, shall constitute a quorum for the consideration
of such question, but a smaller group may adjourn any meeting from time to time.
When a quorum is present at any meeting, a majority of the stock represented
thereat and entitled to vote shall, except where a larger vote is required by
law, by the certificate of incorporation, or by these by-laws, decide any
question brought before such meeting. Any election by stockholders shall be
determined by a plurality of the vote cast by the stockholders entitled to vote
at the election.

      SECTION 7. Proxies and Voting. Each stockholder shall at every meeting of
the stockholders be entitled to one vote in person or by proxy for each share of
the capital stock held of record by such stockholder, but no proxy shall be
voted on after three years from its date, unless said proxy provides for a
longer period. Persons holding stock in a fiduciary capacity shall be entitled
to vote the shares so held, and persons whose stock is pledged shall be entitled
to vote, unless in the transfer by the pledgor on the books of the corporation
the pledgee shall have been expressly empowered to vote thereon, in which case
only the pledgee or the pledgee's proxy may represent said stock and vote
thereon. Shares of the capital stock of the corporation belonging to the
corporation or to another corporation, a majority of whose shares entitled to
vote in the election of directors is owned by the corporation, shall not be
entitled to vote nor counted for quorum purposes.

      SECTION 8. Conduct of Meeting. Meetings of the stockholders shall be
presided over by one of the following officers in the order of seniority and in
present and acting: the Chairman of the Board, if any, the Vice-Chairman of the
Board, if any, the President, a Vice-President, or, if none of the foregoing is
in office and present and acting, a chairman to be chosen by the stockholders.
The Secretary of the corporation, if present, or an Assistant Secretary, shall
act as secretary of every meeting, but if neither the Secretary nor an Assistant
Secretary is present the chairman of the meeting shall appoint a secretary of
the meeting.

      SECTION 9. Action Without Meeting. Any action required or permitted to be
taken at any annual or special meeting of stockholders of the corporation may be
taken without a meeting, without prior notice and without a vote, if a consent
in writing, setting forth the action so taken, is signed by the holders or by
proxy for the holders of outstanding stock having not less than the minimum
number of votes that would be necessary to authorize or take such action at a
meeting at which all shares entitled to vote on such action were present and
voted. Prompt notice of the taking of corporate action without a meeting by less
than unanimous written consent shall be given to those stockholders who have not
consented in writing.


                                   ARTICLE II

                                    DIRECTORS

      SECTION 1. General Powers. The business and affairs of the corporation
shall be managed by or under the direction of a Board of Directors, who may
exercise all of the powers of the corporation which are not by law required to
be exercised by the stockholders. In the event of a vacancy in the Board of
Directors, the remaining directors, except as otherwise provided by law, may
exercise the powers of the full Board until the vacancy is filled.

      SECTION 2. Number; Election; Tenure and Qualification. The initial Board
of Directors shall consist of three persons and shall be elected by the
incorporator. Thereafter, the number of directors which shall constitute the
whole Board shall be fixed by resolution of the stockholders, but in no event
shall be less than one. Each director shall be elected by the stockholders at
the annual meeting and all directors shall hold office until the next annual
meeting and until their successors are elected and qualified, or until their
earlier death, resignation or removal. The number of directors may be increased


                                     - 2 -


or decreased by action of the stockholders. Directors need not be stockholders
of the corporation.

      SECTION 3. Enlargement of the Board. The number of the Board of Directors
may be increased at any time, such increase to be effective immediately, by
resolution of the stockholders.

      SECTION 4. Vacancies. Any vacancy in the Board of Directors, however
occurring, including a vacancy resulting from an enlargement of the Board and an
unfilled vacancy resulting from the removal of any director for cause or without
cause, may be filled by resolution of the stockholders. A director elected to
fill a vacancy shall hold office until the next annual meeting of stockholders
and until his or her successor is elected and qualified or until his or her
earlier death, resignation, or removal. When one or more directors shall resign
from the Board, effective at a future date, the stockholders shall have the
power to fill such vacancy or vacancies, the vote thereon to take effect when
such resignation or resignations shall become effective. If at any time there
are no directors in office, then an election of directors may be held in
accordance with the General Corporation Law of the State of Delaware.

      SECTION 5. Resignation. Any director may resign at any time upon written
notice to the corporation. Such resignation shall take effect at the time
specified therein, or if no time is specified, at the time of its receipt by the
President or Secretary.

      SECTION 6. Removal. Except as may otherwise be provided by the General
Corporation Law, any director or the entire Board of Directors may be removed,
with or without cause, at an annual meeting or at a special meeting called for
that purpose, by the holders of a majority of the shares then entitled to vote
at an election of directors. The vacancy or vacancies thus created may be filled
by the stockholders at the meeting held for the purpose of removal.

      SECTION 7. Committees. The Board of Directors may, by resolution or
resolutions passed by a majority of the whole Board of Directors, designate one
or more committees, each committee to consist of two or more directors of the
corporation. The Board of Directors may designate one or more directors as
alternate members of any committee, who may replace any absent or disqualified
member at any meeting of the committee. In the absence or disqualification of
any member of such committee or committees, the member or members thereof
present at any meeting and not disqualified from voting, whether or not such
member or members constitute a quorum, may unanimously appoint another member of
the Board of Directors to act at the meeting in the place of such absent or
disqualified member.

      A majority of all the members of any such committee may fix its rules of
procedure, determine its action and fix the time and place, whether within or
without the State of Delaware, of its meetings and specify what notice thereof,
if any, shall be given, unless the Board of Directors shall otherwise by
resolution provide. The Board of Directors shall have the power to change the
members of any such committee at any time, to fill vacancies therein and to
discharge any such committee, either with or without cause, at any time.

      Any such committee, unless otherwise provided in the resolution of the
Board of Directors, or in these by-laws, shall have and may exercise all the
powers and authority of the Board of Directors in the management of the business
and affairs of the corporation, and may authorize the seal of the corporation to
be affixed to all papers which may require it; but no such committee shall have
such power or authority in reference to amending the certificate of
incorporation, adopting an agreement of merger or consolidation, recommending to
the stockholders the sale, lease or exchange of all or substantially all of the
corporation's property and assets, recommending a dissolution of the corporation
or a revocation of a dissolution, or amending the by-laws of the corporation,
and, unless the resolution or these by-laws expressly so provide, no such
committee shall have the power or the authority to declare a dividend or to
authorize the issuance of stock.

      Each committee shall keep regular minutes of its meetings and make such
reports as the Board of Directors may from time to time request.

      SECTION 8. Meetings of the Board of Directors. Regular meetings of the
Board of Directors may be held without call or formal notice at such places
either within or without the State of Delaware and at such times as the Board
may by vote form time to time determine. A regular meeting of the Board of
Directors may be held without call or formal notice immediately after and at the


                                     - 3 -


same place as the annual meeting of the stockholders, or any special meeting of
the stockholders at which a Board of Directors is elected.

      Special meetings of the Board of Directors may be held at any place either
within or without the State of Delaware at any time when called by the Chairman
of the Board of Directors, the President, Treasurer, Secretary, or two or more
directors. Reasonable notice of the time and place of a special meeting shall be
given to each director unless such notice is waived by attendance or by written
waiver in the manner provided in these by-laws for waiver of notice of
stockholders. No notice of any adjourned meeting of the Board of Directors shall
be required. In any case it shall be deemed sufficient notice to a director to
send notice by mail at least seventy-two hours, or by telegram at least
forty-eight hours, before the meeting, addressed to such director at his or her
usual or last known business or home address.

      Directors or members of any committee designated by the directors may
participate in a meeting of the Board of Directors or such committee by means of
conference telephone or similar communications equipment by means of which all
persons participating in the meeting can hear each other, and participation by
such means shall constitute presence in person at such meeting.

      SECTION 9. Quorum and Voting. A majority of the total number of directors
shall constitute a quorum, except that when a vacancy or vacancies exist in the
Board, a majority of the directors then in office (but not less than one-third
of the total number of the directors) shall constitute a quorum, and except that
a lesser number of directors consisting of a majority of the directors then in
office who are not officers (but not less than one-third of the total number of
directors) may constitute a quorum for the purpose of acting on any matter
relating to the compensation (including fringe benefits) of an officer of the
corporation. A majority of the directors present, whether or not a quorum is
present, may adjourn any meeting from time to time. The vote of a majority of
the directors present at any meeting at which a quorum is present shall be the
act of the Board of Directors, except where a different vote is required or
permitted by law, by the certificate of incorporation, or by these by-laws.

      SECTION 10. Compensation. The Board of Directors may fix fees for their
services and for their membership on committees, and expenses of attendance may
be allowed for attendance at each meeting. Nothing herein contained shall be
construed to preclude any director from serving the corporation in any other
capacity as an officer, agent or otherwise, and receiving compensation therefor.

      SECTION 11. Action Without Meeting. Any action required or permitted to be
taken at any meeting of the Board of Directors, or of any committee thereof, may
be taken without a meeting, and without notice, if a written consent thereto is
signed by all members of the Board of Directors, or of such committee, as the
case may be, and such written consent is filed with the minutes of proceedings
of the Board of Directors or such committee.


                                   ARTICLE III

                                    OFFICERS

      SECTION 1. Titles. The officers of the corporation shall consist of a
President, a Secretary, a Treasurer, and such other officers with such other
titles as the Board of Directors shall determine, including without limitation a
Chairman of the Board, a Vice-Chairman of the Board, and one or more
Vice-Presidents, Assistant Treasurers, or Assistant Secretaries.

      SECTION 2. Election and Term of Office. The officers of the corporation
shall be elected annually by the Board of Directors at its first meeting
following the annual meeting of the stockholders. Each officer shall hold office
until his or her successor is elected and qualified, unless a different term is
specified in the vote electing such officer, or until his or her earlier death,
resignation or removal.

      SECTION 3. Qualification. Unless otherwise provided by resolution of the
Board of Directors, no officer, other than the Chairman or Vice-Chairman of the
Board, need be a director. No officer need be a stockholder. Any number of
offices may be held by the same person, as the directors shall determine, but no
person may hold the offices of President and Secretary simultaneously.


                                     - 4 -


      SECTION 4. Removal. Any officer may be removed, with or without cause, at
any time, by resolution adopted by the Board of Directors.

      SECTION 5. Resignation. Any officer may resign by delivering a written
resignation to the corporation at its principal office or to the President or
Secretary. Such resignation shall be effective upon receipt or at such later
time as shall be specified therein.

      SECTION 6. Vacancies. The Board of Directors may at any time fill any
vacancy occurring in any office for the unexpired portion of the term and may
leave unfilled for such period as it may determine any office other than those
of President, Treasurer and Secretary.

      SECTION 7. Powers and Duties. The officers of the corporation shall have
such powers and perform such duties as are specified herein and as may be
conferred upon or assigned to them by the Board of Directors, and shall have
such additional powers and duties as are incident to their office except to the
extent that resolutions of the Board of Directors are inconsistent therewith.

      SECTION 8. President and Vice-Presidents. The President shall be the chief
executive officer of the corporation, shall preside at all meetings of the
stockholders and the Board of Directors unless a Chairman or Vice-Chairman of
the Board is elected by the Board, empowered to preside, and present at such
meeting, shall have general and active management of the business of the
corporation and general supervision of its officers, agents and employees, and
shall see that all orders and resolutions of the Board of Directors are carried
into effect.

      In the absence of the President or in the event of his or her inability or
refusal to act, the Vice-President if any (or in the event there be more than
one Vice-President, the Vice-Presidents in the order designated by the
directors, or in the absence of any designation, then in the order of their
election) shall perform the duties of the President, and when so acting, shall
have all the powers of and be subject to all the restrictions upon the
President. The Board of Directors may assign to any Vice-President the title of
Executive Vice-President, Senior Vice-President or any other title selected by
the Board of Directors.

      SECTION 9. Secretary and Assistant Secretaries. The Secretary shall attend
all meetings of the Board of Directors and of the stockholders and record all
the proceedings of such meetings in a book to be kept for that purpose, shall
give, or cause to be given, notice of all meetings of the stockholders and
special meetings of the Board of Directors, shall maintain a stock ledger and
prepare lists of stockholders and their addresses as required and shall have
custody of the corporate seal which the Secretary or any Assistant Secretary
shall have authority to affix to any instrument requiring it and attest by any
of their signatures. The Board of Directors may give general authority to any
other officer to affix and attest the seal of the corporation.

      The Assistant Secretary if any (or if there be more than one, the
Assistant Secretaries in the order determined by the Board of Directors of if
there be no such determination, then in the order of their election) shall, in
the absence of the Secretary or in the event of the Secretary's inability or
refusal to act, perform the duties and exercise the powers of the Secretary.

      SECTION 10. Treasurer and Assistant Treasurers. The Treasurer shall have
the custody of the corporate funds and securities, shall keep full and accurate
accounts of receipts and disbursements in books belonging to the corporation and
shall deposit all moneys and other valuable effects in the name and to the
credit of the corporation in such depositories as may be designated by the Board
of Directors. The Treasurer shall disburse the funds of the corporation as may
be ordered by the Board of Directors or the President, taking proper vouchers
for such disbursements, and shall render to the President and the Board of
Directors, at its regular meetings, or whenever they may require it, an account
of all transactions and of the financial condition of the corporation.

      The Assistant Treasurer if any (or if there be more than one, the
Assistant Treasurers in the order determined by the Board of Directors or if
there be no such determination, then in the order of their election) shall, in
the absence of the Treasurer or in the event of his or her inability or refusal
to act, perform the duties and exercise the powers of the Treasurer.


                                     - 5 -


      SECTION 11. Bonded Officers. The Board of Directors may require any
officer to give the corporation a bond in such sum and with such surety or
sureties as shall be satisfactory to the Board of Directors upon such terms and
conditions as the Board of Directors may specify, including without limitation a
bond for the faithful performance of the duties of such officer and for the
restoration to the corporation of all property in his or her possession or
control belonging to the corporation.

      SECTION 12. Salaries. Officers of the corporation shall be entitled to
such salaries, compensation or reimbursement as shall be fixed or allowed from
time to time by the Board of Directors.


                                   ARTICLE IV

                                      STOCK

      SECTION 1. Certificates of Stock. One or more certificates of stock,
signed by the Chairman or Vice-Chairman of the Board of Directors or by the
President or Vice-President and by the Treasurer or an Assistant Treasurer or
the Secretary or an Assistant Secretary, shall be issued to each stockholder
certifying, in the aggregate, the number of shares owned by the stockholder in
the corporation. Any or all signatures on any such certificate may be facsimile.
In case any officer who shall have signed or whose facsimile signature shall
have been placed upon a certificate shall have ceased to be such officer before
such certificate is issued, it may be issued by the corporation with the same
effect as if he were such officer at the date of issue.

      Each certificate for shares of stock which are subject to any restriction
on transfer pursuant to the certificate of incorporation, the by-laws,
applicable securities laws, or any agreement among any number of shareholders or
among such holders and the corporation shall have conspicuously noted on the
face or back of the certificate either the full text of the restriction or a
statement of the existence of such restriction.

      SECTION 2. Transfer of Share of Stock. Subject to the restrictions, if
any, stated or noted on the stock certificates, shares of stock may be
transferred on the books of the corporation by the surrender to the corporation
or its transfer agent of the certificate representing such shares properly
endorsed or accompanied by a written assignment or power of attorney properly
executed, and with such proof of authority or the authenticity of signature as
the corporation or its transfer agent may reasonably require. The corporation
shall be entitled to treat the record holder of stock as shown on its books as
the owner of such stock for all purposes, including the payment of dividends and
the right to vote with respect to that stock, regardless of any transfer, pledge
or other disposition of that stock, until the shares have been transferred on
the books of the corporation in accordance with the requirements of these
by-laws.

      SECTION 3. Lost Certificates. A new certificate of stock may be issued in
the place of any certificate theretofore issued by the corporation and alleged
to have been lost, stolen, destroyed, or mutilated, upon such terms in
conformity with law as the Board of Directors shall prescribe. The directors
may, in their discretion, require the owner of the lost, stolen, destroyed or
mutilated certificate, or the owner's legal representatives, to give the
corporation a bond, in such sum as they may direct, to indemnify the corporation
against any claim that may be made against it on account of the alleged loss,
theft, destruction or mutilation of any such certificate, or the issuance of any
such new certificate.

      SECTION 4. Record Date. The Board of Directors may fix in advance a record
date for the determination of the stockholders entitled to notice of or to vote
at any meeting of stockholders or to express consent to corporate action in
writing without a meeting, or entitled to receive payment of any dividend or
other distribution or allotment of any rights in respect of any change,
conversion or exchange of stock, or for the purpose of any other lawful action.
Such record date shall not be more than 60 nor less than 10 days before the date
of such meeting, nor more than 60 days prior to any other action to which such
record date relates.

      If no record date is fixed, the record date for determining stockholders
entitled to notice of or to vote at a meeting of stockholders shall be at the
close of business on the day before the day on which notice is given, or, if
notice is waived at the close of business on the day before the day on which the
meeting is held. The record date for determining stockholders entitled to
express consent to corporate action in writing without a meeting, when no prior
action by the Board of Directors is necessary, shall be the day on which the
first written consent is expressed. The record date for determining stockholders


                                     - 6 -


for any other purpose shall be at the close of business on the day on which the
Board of Directors adopts the resolution relating to such purpose.

      A determination of stockholders of record entitled to notice of or to vote
at a meeting of stockholders shall apply to any adjournment of the meeting;
provided, however, that the Board of Directors may fix a new record date for the
adjourned meeting.

      SECTION 5. Fractional Share Interests. The corporation may, but shall not
be required to, issue fractions of a share. If the corporation does not issue
fractions of a share, it shall (1) arrange for the disposition of fractional
interests by those entitled thereto, (2) pay in cash the fair value of fractions
are determined, or (3) issue scrip or warrants in registered or bearer form
which shall entitle the holder to receive a certificate for a full share upon
the surrender of such scrip or warrants aggregating a full share. A certificate
for a fractional share shall, but scrip or warrants shall not unless otherwise
provided therein, entitle the holder to exercise voting rights, to receive
dividends thereon, and to participate in any of the assets of the corporation in
the event of liquidation. The Board of Directors may cause scrip or warrants to
be issued subject to the conditions that they shall become void if not exchanged
for certificates representing full shares before a specified date, or subject to
the conditions that the shares for which scrip or warrants are exchangeable may
be sold by the corporation and the proceeds thereof distributed to the holders
of scrip or warrants, or subject to any other conditions which the Board of
Directors may impose.

      SECTION 6. Dividends. Subject to the provisions of the certificate of
incorporation, the Board of Directors may, out of funds legally available
therefor, at any regular or special meeting, declare dividends upon the common
stock of the corporation as and when they deem expedient.


                                    ARTICLE V

                          INDEMNIFICATION AND INSURANCE

      SECTION 1. Indemnification. The corporation shall, to the full extent
permitted by the General Corporation Law of the State of Delaware, as amended
from time to time, and the certificate of incorporation, indemnify each person
whom it may indemnify pursuant thereto.

      SECTION 2. Insurance. The corporation shall have power to purchase and
maintain insurance on behalf of any person who is or was a director, officer,
employee or agent of the corporation, or is or was serving at the request of the
corporation as a director, officer, employee or agent of another corporation,
partnership, joint venture, trust or other enterprise against any liability
asserted against such person and incurred by such person in any capacity or
arising out of such person's status as such, whether or not the corporation
would have the power to indemnify such person against such liability under the
provisions of the General Corporation Law of the State of Delaware.


                                   ARTICLE VI

                               GENERAL PROVISIONS

      SECTION 1. Fiscal Year. Except as otherwise designated from time to time
by the Board of Directors, the fiscal year of the corporation shall begin on the
first day of April and end on the last day of March.

      SECTION 2. Corporate Seal. The corporate seal shall be in such form as
shall be approved by the Board of Directors. The Secretary shall be the
custodian of the seal. The Board of Directors may authorize a duplicate seal to
be kept and used by any other officer.

      SECTION 3. Certificate of Incorporation. All references in these by-laws
to the certificate of incorporation shall be deemed to refer to the certificate
of incorporation of the corporation, as in effect from time to time.


                                     - 7 -


      SECTION 4. Execution of Instruments. The President, any Vice-President, or
the Treasurer shall have power to execute and deliver on behalf and in the name
of the corporation any instrument requiring the signature of an officer of the
corporation, including deeds, contracts, mortgages, bonds, notes, debentures,
checks, drafts, and other orders for the payment of money. In addition, the
Board of Directors may expressly delegate such powers to any other officer or
agent of the corporation.

      SECTION 5. Voting of Securities. Except as the directors may otherwise
designate, the President or Treasurer may waive notice of, and act as, or
appoint any person or persons to act as, proxy or attorney-in-fact for this
corporation (with or without power of substitution) at any meeting of
stockholders or shareholders of any other corporation or organization the
securities of which may be held by this corporation.

      SECTION 6. Evidence of Authority. A certificate by the Secretary, or an
Assistant Secretary, or a temporary secretary, as to any action taken by the
stockholders, directors, a committee or any officer or representative of the
corporation shall, as to all persons who rely on the certificate in good faith,
be conclusive evidence of that action.

      SECTION 7. Transactions with Interested Parties. No contract or
transaction between the corporation and one or more of the directors or
officers, or between the corporation and any other corporation, partnership,
association, or other organization in which one or more of the directors or
officers are directors or officers, or have a financial interest, shall be void
or voidable solely for that reason, or solely because the director or officer is
present at or participates in the meeting of the Board of Directors or a
committee of the Board of Directors which authorizes the contract or transaction
or solely because the vote of any such director is counted for such purpose, if:

            (1) The material facts as to the relationship or interest and as to
      the contract or transaction are disclosed or are known to the Board of
      Directors or the committee, and the Board or committee in good faith
      authorizes the contract or transaction by the affirmative votes of a
      majority of the disinterested directors, even though the disinterested
      directors be less than a quorum; or

            (2) The material facts as to the relationship or interest and as to
      the contract or transaction are disclosed or are known to the stockholders
      entitled to vote therein, and the contract or transaction is approved by
      the stockholders; or

            (3) The contract or transaction is fair as to the corporation as of
      the time it is authorized, approved or ratified by the Board of Directors,
      a committee of the Board of Directors, or the stockholders.

      Common or interested directors may be counted in determining the presence
of a quorum at a meeting of the Board of Directors or of a committee which
authorizes the contract or transaction.

      SECTION 8. Books and Records. The books and records of the corporation
shall be kept at such places within or without the State of Delaware as the
Board of Directors may from time to time determine.


                                   ARTICLE VII

                                   AMENDMENTS

      SECTION 1. By the Stockholders. These by-laws may be altered, amended or
repealed or new by-laws may be adopted by the affirmative vote of the holders of
a majority of the shares of the capital stock of the corporation issued and
outstanding and entitled to vote at any regular meeting of stockholders, or at
any special meeting of stockholders provided notice of such alteration,
amendment, repeal or adoption of new by-laws shall have been stated in the
notice of such special meeting.



                                      *****


                                     - 8 -


          Resolution of the Board of Directors of Repligen Corporation


                    Amending the Repligen Corporation By-Laws

      That the Board of Directors of Repligen Corporation (the "Corporation"),
duly and validly adopted the following resolutions at a meeting of the Board of
Directors on June 25, 2003:

RESOLVED:  That the Board of Directors recommend to the stockholders that
           Article II, Section 3 of the By-Laws of the Corporation (the
           "By-Laws") be amended and restated in its entirety to allow
           vacancies on the Board of Directors to be filled by action of
           the Board of Directors in the following form:

                    Section 4. Vacancies. Any vacancy in the Board of
           Directors, however occurring, including a vacancy resulting
           from an enlargement of the Board and an unfilled vacancy
           resulting from an enlargement of the Board and an unfilled
           vacancy resulting from the removal of any director for cause
           or without cause, may be filled by resolution of the Board. A
           director elected to fill a vacancy shall hold office until the
           next annual meeting of stockholders and until his or her
           successor is elected and qualified or until his or her earlier
           death, resignation or removal. When one or more directors
           shall resign from the Board, effective at a future date, the
           Board, shall have the power to fill such vacancy or vacancies,
           the vote thereon to take effect when such resignation or
           resignations shall become effective. If at any time there are
           no directors in office, then an election of directors may be
           held in accordance with the General Corporation Law of the
           State of Delaware.

RESOLVED:  That the foregoing amendment to the By-Laws is hereby declared
           to be advisable and in the best interests of the Corporation
           and its stockholders, and that the appropriate officers of the
           Corporation be, and each of them acting singly hereby is,
           authorized and directed to present such proposed amendment to
           the stockholders of the Corporation for their approval at the
           next Annual Meeting of Stockholders.


                                     - 9 -


                                                                      Appendix B


            AMENDED AND RESTATED 2001 REPLIGEN CORPORATION STOCK PLAN


      1. Purpose of the Plan; Compliance with Rule 16b-3.

      (a) The Amended and Restated 2001 Repligen Corporation Stock Plan (the
"Plan") is intended as an incentive to, and to encourage ownership of the stock
of Repligen Corporation, a Delaware corporation (the "Company") by, qualified
employees, outside directors and consultants of the Company and its
subsidiaries. It is intended that certain options granted thereunder will
qualify as incentive stock options (the "Incentive Stock Options") within the
meaning of Section 422 of the Internal Revenue Code of 1986, as amended (the
"Code") and that other options granted thereunder will not qualify as Incentive
Stock Options. Of such latter options, certain options will be granted in the
sole discretion of the Committee referred to in Section 4 hereof (the
"Committee") and certain other options (the "Board Options") will be granted to
non-employee members of the Board of Directors of the Company (the "Board of
Directors") in accordance with the provisions of Section 5 hereof. Restricted
Stock Awards (as defined below) may also be granted under the Plan.

      (b) With respect to persons subject to Section 16 of the Securities
Exchange Act of 1934, as amended (the "1934 Act"), transactions thereunder are
intended to comply with all applicable conditions of Rule 16b-3 or its
successors under the 1934 Act. To the extent that any provision of the Plan or
action of the Committee fails to so comply, it shall be deemed null and void, to
the extent permitted by law and (in the case of Incentive Stock Options,
Non-Qualified Options and Restricted Stock Awards, each an "Award") deemed
advisable by the Committee.

      2. Common Stock Subject to the Plan.

      (a) The aggregate number of shares of the Company's Common Stock, par
value $0.01 per share, that may be issued pursuant to the Plan is 1,585,778
shares. To the extent that options previously granted under the 1992 Repligen
Corporation Stock Option Plan, as amended (collectively, the "Prior Plan")
expire or terminate for any reason without having been exercised after the
termination of the Prior Plan, then options exercisable for that same number of
shares of Common Stock or Restricted Stock Awards, up to a maximum of 1,663,841
shares, may be granted pursuant to the Plan. If any Award granted under the Plan
shall expire or terminate for any reason without having been exercised in full,
the unexercised shares subject thereto shall again be available for issuance
pursuant to the provisions of the Plan. Subject to the provisions of Section
15(c), the maximum number of shares of Common Stock which may be issued in
accordance with the provisions of this Section 2(a) shall be 3,249,619.

      (b) The Company may, in its discretion, use shares held in the treasury in
lieu of authorized but unissued shares.

      3. Administration.

      The Plan shall be administered by the Committee; provided, that with
respect to the Board Options, the price, amount and timing of such options shall
be solely as set forth in Section 5 below.

      4. The Committee; Issuance of Incentive Stock Options, Non-Qualified
Options and Restricted Stock Awards.

      (a) The Committee shall at all times be constituted to permit transactions
thereunder to comply with Rule 16b-3 under the 1934 Act, or any successor to
such Rule, and will consist of two or more "outside directors" (as defined in
the applicable regulations promulgated under Section 162(m) of the Code). The
Committee shall be appointed by the Board of Directors, which may from time to
time appoint members of the Committee in substitution for members previously


                                     - 1 -


appointed and may fill vacancies, however caused, in the Committee. The
Committee may select one of its members as its Chairman, and shall hold its
meetings at such times and places as it may determine. A majority of its members
(or both of its members, if there are only two) shall constitute a quorum. All
determinations of the Committee shall be made by a majority of its members, or,
if there are only two members, by unanimous vote. Any decision or determination
reduced to writing and signed by a majority (or if there are only two, both) of
the members shall be fully as effective as if it had been made by a majority (or
unanimous, as the case may be) vote at a meeting duly called and held. The
Committee may appoint a secretary, shall keep minutes of its meetings and shall
make such rules and regulations for the conduct of its business as it shall deem
advisable.

      (b) Subject to the express provisions of the Plan, the Committee shall
have plenary authority, in its discretion, to determine the individuals to whom,
and the time or times at which, Incentive Stock Options and Non-Qualified
Options, or Restricted Stock Awards shall be granted, the number of shares to be
subject to each such Award, the duration of each such option, the exercise or
purchase price and method of payment, the times or time within which (during the
term of the option) all or portions of each such Award may be exercised, as
applicable, and the terms, conditions and restrictions of Restricted Stock
Awards. In making such determinations the Committee may take into account the
nature of the services rendered by the respective individuals, their present and
potential contributions to the Company's success and such other factors as the
Committee, in its discretion, shall deem relevant. Subject to the express
provisions of the Plan, the Committee shall also have plenary authority to
interpret the Plan to prescribe, amend and rescind rules and regulations
relating thereto, to determine the terms and provisions of the respective stock
option agreements in accordance with Section 9 hereof and to make all other
determinations necessary or advisable for the administration of the Plan. The
Committee's determinations on the matters referred to in this Section 4(b) shall
be conclusive. The Committee shall not have any discretionary authority with
respect to the award or terms and conditions of the Board Options.

      (c) The Committee may grant eligible persons the right to acquire shares
of Common Stock, subject to (i) delivery to the Company by the recipient of cash
or other lawful consideration in an amount at least equal to the par value of
the shares purchased, and (ii) the right of the Company to repurchase all or
part of such shares at their issue price or other stated or formula price from
the recipient in the event that conditions specified by the Committee in the
applicable Award are not satisfied prior to the end of the applicable
restriction period or periods established by the Committee for such Award (each,
a "Restricted Stock Award").

      (d) The Committee shall determine the terms and conditions of any such
Restricted Stock Award, including the effect on a Restricted Stock Award (and
Common Stock acquired pursuant to such Restricted Stock Award) of the
disability, death, retirement, authorized leave of absence or other change in
the employment or other status of the recipient. Any stock certificates issued
in respect of a Restricted Stock Award shall be registered in the name of the
recipient and, unless otherwise determined by the Committee, deposited by the
recipient, together with a stock power endorsed in blank, with the Company (or
its designee). After the expiration of the applicable restriction periods, the
Company (or its designee) shall deliver the certificates no longer subject to
such restrictions to the recipient or, if the recipient has died, to the
beneficiary designated by a recipient, in a manner determined by the Committee,
to receive amounts due or exercise rights of the recipient in the event of the
recipient's death (the "Designated Beneficiary"). In the absence of an effective
designation by a recipient, Designated Beneficiary shall mean the recipient's
estate.


      5. Issuance of Board Options.

      Subject to the limitations set forth in this Section 5, (i) each
non-employee director of the Company, for so long as such person remains a
non-employee director of the Company, shall be entitled to receive an annual
option to purchase 15,000 shares of Common Stock to vest in full on the first


                                     - 2 -


anniversary of the date of the grant, provided such person is still a director
on such anniversary and (ii) each person who becomes a member of the Board of
Directors who is not employed by the Company after the effective date of the
Plan shall receive, at the time such person first becomes a member of the Board
of Directors, an option to purchase 24,000 shares of Common Stock, vesting
equally over a three-year period from the date of grant. Notwithstanding
anything to the contrary contained herein, no person shall be entitled to
receive Board Options pursuant to the Plan covering more than an aggregate
150,000 shares, excluding such Board Options that have expired without being
exercised. Those options granted to non-employee directors pursuant to this
Section 5 are referred to herein as "Board Options."

      6. Eligibility.

      (a) Incentive Stock Options may be granted only to employees of the
Company or a subsidiary.

      (b) Non-Qualified Options may be granted only to (i) officers (who may
also be directors) and full or part-time employees employed on a salaried or
commission basis by the Company or its subsidiaries, (ii) members of the Board
of Directors of the Company who are not included within the group of individuals
referenced in the foregoing clause, and (iii) any individual performing services
for the Company or any subsidiary as an independent contractor pursuant to a
written or oral agreement with the Company or a subsidiary.

      (c) Board Options may be granted only to members of the Board of Directors
of the Company who are not employees of either the Company or its subsidiaries.

      (d) Restricted Stock Awards may be granted to directors and officers of
the Company and full-time employees employed on a salaried or commission basis
by the Company or its subsidiaries, as well as any individual performing
services for the Company or any subsidiary as an independent contractor.

      (e) For purposes of the Plan, the term "subsidiary" shall mean any
corporation (other than the Company) in an unbroken chain of corporations
beginning with the Company if, at the time of the granting of the option, each
of the corporations other than the last corporation in the unbroken chain owns
stock possessing 50% or more of the total combined voting power of all classes
of stock in one of the other corporations in such chain, or such other meaning
as may be hereafter ascribed to it in Section 424 of the Code.

      7. Exercise and Purchase Prices of Awards.

      (a) The purchase price of the Common Stock under each Incentive Stock
Option shall not be less than 100% of the fair market value of the stock at the
time of the granting of the option. For purposes hereof, fair market value shall
be equal to the NASDAQ National Market closing price (or the closing price on an
exchange if the Common Stock is then traded on an exchange) per share of Common
Stock for the day as of which an Incentive Stock Option is granted, or such
other amounts (which may be different amounts as between the various types of
options) as shall be determined from time to time in good faith by the Committee
pursuant to such criteria as it may determine to be appropriate.

      (b) The purchase price of the Common Stock under each Non-Qualified Option
shall not be less than the par value of the Common Stock.

      (c) The purchase price of the Common Stock under each Board Option shall
be equal to the average NASDAQ National Market System closing price (or the
average closing price on an exchange if the Common Stock is then traded on an
exchange) per share of Common Stock for the thirty (30) trading days immediately
preceding the date of the grant of such Board Option.

      (d) Incentive Stock Options and Non-Qualified Options may be exercised, in
the discretion of the Committee, by payment of the option price in full (i) in
cash, (ii) by surrender of shares of the capital stock of the Company having a


                                     - 3 -


fair market value equal to the option price on the date of exercise, or (iii)
any combination of the foregoing. Board Options may be exercised by payment of
the option price in full by means of any of the three methods of payment
specified in the preceding sentence.

      (e) The purchase price of the Common Stock under each Restricted Stock
Award may not be less than the par value of Common Stock.

      (f) The proceeds of sale of stock subject to Awards are to be added to the
general funds of the Company or to the shares of the Common Stock of the Company
held in its treasury, and used for its corporate purposes as the Board of
Directors shall determine.

      (g) Notwithstanding any provision herein to the contrary, no Incentive
Stock Option shall be granted to any individual whose ownership of Common Stock
of the Company or one of its subsidiaries exceeds the limitations set forth in
Section 422(b)(6) of the Code unless such option price is at least 110% of the
fair market value of the stock at the time of the granting of the option.

      8. Award Amounts.

      (a) The maximum aggregate fair market value (determined at the time an
option is granted in the same manner as provided for in Section 7(a) hereof) of
the Common Stock of the Company with respect to which Incentive Stock Options
are exercisable for the first time by any optionee during any calendar year
(under all plans of the Company and its subsidiaries) shall not exceed $100,000.

      (b) No optionee may be granted Awards to acquire, in the aggregate more
than 1,500,000 shares of Common Stock under the Plan during any fiscal year of
the Company.

      9. Form of Awards.

      Incentive Stock Options, Non-Qualified Options, Restricted Stock Awards
and Board Options shall be in such form conforming to applicable legal
requirements as shall be approved from time to time by the Committee. The form
of any such Awards may vary among the recipients.

      10. Term of Options; Exercise of Options.

      (a) The term of each option shall be not more than ten (10) years from the
date of granting thereof, provided that no Incentive Stock Option shall be
granted to any individual whose ownership of Common Stock of the Company or its
subsidiaries exceeds the limitations set forth in Section 422(b)(6) of the Code
unless the term of his or her option does not exceed a period of five (5) years
from the date of the grant, or such shorter period as is prescribed in Section
10 hereof.

      (b) Within the limits specified in Section 10(a) hereof, Incentive Stock
Options and Non-Qualified Options will be exercisable at such time or times, and
subject to such restrictions and conditions, as the Committee shall, in each
instance, approve, which need not be uniform for all optionees; provided,
however, that except as provided in Sections 11 and 12 hereof, no such option
granted to an employee of the Company or a subsidiary may be exercised at any
time unless the optionee is then an employee of the Company or a subsidiary and
has been so employed continuously since the granting of the option.

      (c) Notwithstanding any provision to the contrary contained herein, upon
the removal or resignation from the Board of Directors of a holder of a Board
Option, such holder may exercise such Board Option within three (3) months of
such holder's resignation or removal (but in any case not after ten (10) years
from the date of the granting of the option) to the same extent that such holder
was entitled to exercise it as of the date of such resignation or removal.

      (d) The holder of an option shall have none of the rights of a stockholder
with respect to the shares subject to option until such shares shall be issued
to such holder upon the exercise of such holder's option.


                                     - 4 -


      (e) With respect to persons subject to Section 16 under the 1934 Act,
options granted thereunder must be held by the optionee for at least six (6)
months from the date of grant to the date of disposition of the option (other
than by exercise) or the Common Stock underlying such option.

      11. Termination of Employment.

      (a) Any employee of the Company or a subsidiary who has been issued an
option thereunder must exercise the option prior to such employee's termination
of employment, except that if an employee terminates their employment
voluntarily, such employee shall be permitted to exercise any such option then
held by them at any time within three (3) months after such termination (but in
any case not after ten (10) years from the date of the granting thereof) to the
same extent that such employee was entitled to exercise it at the date of such
termination of employment.

      (b) If the holder of an Incentive Stock Option or a Non-Qualified Option
terminates employment on account of disability such holder may exercise such
option to the extent such holder was entitled to exercise it at the date of such
termination at any time within one (1) year of the termination of such holder's
employment (but in any case not after ten (10) years from the date of the
granting thereof). For this purpose a person shall be deemed to be disabled if
such holder is permanently and totally disabled within the meaning of Section
422(c)(6) of the Code, which, as of the date hereof, shall mean that such holder
is unable to engage in any substantial gainful activity by reason of any
medically determined physical or mental impairment which can be expected to
result in death or which has lasted or can be expected to last for a period of
not less than 12 months. A person shall be considered disabled only if such
holder furnishes such proof of disability as the Committee may require.

      (c) If the holder of an Incentive Stock Option or Non-Qualified Option
issued thereunder retires on or after the attainment of age sixty-five (65),
such options may be exercised as determined by the Committee but in no event
more than ten (10) years after the date of granting thereof.

      (d) If the employment of the holder of an Incentive Stock Option or
Non-Qualified Option is terminated for "cause," all such options not yet
exercised shall be exercisable within seven (7) days of such termination, and
shall thereafter cease to be of any further force or effect. For purposes of the
foregoing, "cause" shall have the meaning set forth from time to time in the
employee handbook generally distributed by the Company to its employees.

      (e) Incentive Stock Option and Non-Qualified Options granted under the
Plan shall not be affected by any change of employment so long as the holder
thereof continues to be an employee of the Company or a subsidiary of the
Company. The option agreements relating to Incentive Stock Options and
Non-Qualified Options may contain such provisions as the Committee shall approve
with reference to the effect of approved leaves of absence. Nothing in the Plan
or in any Incentive Stock Option or Non-Qualified Option granted pursuant to the
Plan shall confer on any individual any right to continue in the employ of the
Company or a subsidiary of the Company or interfere in any way with the right of
the Company or a subsidiary of the Company to terminate such individual's
employment at any time.

      12. Death of Holder of Option.

      In the event of the death of an individual to whom an Incentive Stock
Option or Non-Qualified Option has been granted under the Plan, while such
individual is employed by the Company (or a subsidiary of the Company) or within
three (3) months after the termination of such individual's employment (or one
(1) year in the case of the termination of employment of an option holder who is
disabled as above provided), the Incentive Stock Option or Non-Qualified Option
heretofore granted to such individual may be exercised, to the extent that such
individual was entitled to exercise it at the date of such death, by a legatee


                                     - 5 -


or legatees of the option holder under such individual's last will, or by his
personal representatives or distributees, at any time within a period of two (2)
years after such individual's death (but in any case not after ten (10) years
from the date of granting thereof), and only if and to the extent that such
individual was entitled to exercise the option at the date of such individual's
death.

      13. Non-Transferability of Awards.

      Each option granted under the Plan shall, by its terms, be
non-transferable otherwise than by will or the laws of descent and distribution
and an option may be exercised, during the lifetime of the holder thereof, only
by such holder. Restricted Stock Awards (and the Common Stock issued thereunder)
shall be subject to such restrictions on transfer as set forth in such Awards.

      14. Successive Award Grants.

      Successive Award grants may be made to any holder of Awards under the
Plan.

      15. Adjustments Upon Changes in Capitalization or Corporate Acquisitions.

      (a) In the event of a consolidation or merger of the Company with another
corporation, or the sale or exchange of all or substantially all of the assets
of the Company, or a separation, reorganization or liquidation of the Company,
each holder of an outstanding option issued in accordance herewith shall be
entitled to receive upon exercise and payment in accordance with the option's
terms the same shares, securities or property as such holder would have been
entitled to receive upon the occurrence of such event if such holder had been,
immediately prior to such event, the holder of the number of shares of Common
Stock purchasable under such holder's option, or, if another corporation shall
be the survivor, such corporation shall substitute therefor substantially
equivalent shares, securities or property of such other corporation; provided,
however, in lieu of the foregoing the Committee may upon written notice to each
holder of an outstanding Incentive Stock Option or Non-Qualified Option provide
that such option (but not a Board Option) shall terminate on a date not less
than twenty (20) days after the date of such notice unless theretofore
exercised. In connection with such notice, the Committee may in its discretion
accelerate or waive any deferred exercise period. The Committee may provide in
the terms of a Restricted Stock Award that some or all restrictions contained in
such Award may terminate upon the occurrence of an event described in this
Section 15(a).

      (b) In the event the Company or a subsidiary of the Company enters into a
transaction described in Section 424(a) of the Code with any other corporation,
the Committee may grant Awards to employees or former employees of such
corporation in substitution of Awards previously granted to them upon such terms
and conditions as shall be necessary to qualify such grant as a substitution
described in Section 424(a) of the Code.

      (c) The number of shares of Common Stock for which Awards may be granted
thereunder and any references to specific amounts of shares (including but not
limited to those references set forth in Sections 5 and 8 hereof) shall be
appropriately adjusted if the number of outstanding shares of Common Stock of
the Company is increased or reduced by split-up, reclassification, stock
dividend or the like. The number of shares previously optioned thereunder and
not theretofore delivered and the option price per share shall likewise be
adjusted whenever the number of outstanding shares of Common Stock is increased
or reduced by any such procedure.

      16. Amendment and Termination.

      (a) The Board of Directors may at any time terminate the Plan, or make
such modifications of the Plan as it shall deem advisable; provided, however,
that the Board of Directors may not, without further approval by a majority of
the holders of Common Stock: (i) increase the maximum number of shares as to


                                     - 6 -


which Awards may be granted under the Plan (except under the anti-dilution
provisions contained in Section 15 hereof); (ii) change the class of persons to
whom Awards may be granted; (iii) withdraw the authority to administer the Plan
(insofar as it relates to Incentive Stock Options, Non-Qualified Options and
Restricted Stock Awards) from the Committee; (iv) extend the duration of the
Plan; (v) provide for any discretion to be vested in the Committee or any other
entity with respect to the award of the Board Options; or (vi) materially
increase the benefits accruing to persons subject to Section 16 of the 1934 Act.
No termination or amendment of the Plan may, without the consent of the person
to whom any Award shall theretofore have been granted, adversely affect the
rights of such person under such Award.

      (b) The provisions of this Plan relating to the Board Options shall not be
amended more than once every six months, other than to comport with changes in
the Code, the Employee Retirement Income Security Act of 1974, as amended, or
the respective rules thereunder.

      17. Effectiveness of the Plan.

      The Plan shall become effective on September 14, 2001 subject, however, to
its approval by the stockholders of the Company given at the annual meeting of
stockholders on September 13, 2001. The amended and restated Plan shall become
effective on September 11, 2003 subject, however, to its approval by the
stockholders of the Company given at the annual meeting of stockholders on
September 10, 2003.

      18. Withholding of Applicable Taxes.

      The Company shall be entitled to withhold the amount of any tax
attributable to any shares deliverable under this Plan after giving the person
entitled to receive such shares notice as far in advance as practicable, and the
Company may defer making delivery if any such tax may be pending unless and
until indemnified to its satisfaction. Alternatively, the Company shall have the
right to reduce the number of shares otherwise required to be delivered upon
exercise of an option granted thereunder by an amount which would have a fair
value on the date of such exercise equal to all taxes required to be withheld by
the Company with respect to such exercise. In connection with such withholding,
the Company may make any such arrangements as are consistent with this Plan as
it may deem appropriate.

      19. Time of Granting of Awards.

      (a) A grant of an Award under the Plan shall be deemed to be made on the
date on which the Committee, by formal action of its members duly recorded in
the records thereof, makes an award of an option or a Restricted Stock Award
(but in no event prior to the adoption of the Plan by the Board of Directors);
provided, that such option or Restricted Stock Award is evidenced by a written
agreement duly executed on behalf of the Company and on behalf of the recipient
within a reasonable time after the date of the Committee action.

      (b) A grant of a Board Option shall be deemed to be made on the applicable
dates provided in Section 5 hereof.

      20. Term of Plan.

The Plan shall terminate ten (10) years after the date on which it is approved
and adopted by the Board of Directors and no Awards shall be granted thereunder
after the expiration of such ten-year period. Awards outstanding at the
termination of the Plan shall continue in full force and effect and shall not be
affected thereby.


                                     - 7 -


-------------------------------------------------------------------------------
If you have questions or need assistance voting your shares contact:


                                    MACKENZIE
                                 PARTNERS, INC.

                               105 Madison Avenue
                            New York, New York 10010
                           proxy@mackenziepartners.com
                          Call Collect: (212) 929-5500
                                       or
                            Toll-Free (800) 322-2885
-------------------------------------------------------------------------------



Dear Stockholder:

Please take note of the important information enclosed with this Proxy. There
are a number of issues related to the operation of the Company that require your
immediate attention.

Your vote counts, and you are strongly encouraged to exercise your right to vote
your shares.

Please mark the boxes on the proxy card to indicate how your shares will be
voted. Then sign the card, detach it and return your proxy in the enclosed
postage paid envelope. Thank you in advance for your prompt consideration of
these matters.

Sincerely,


Repligen Corporation

                                      PROXY
                              REPLIGEN CORPORATION
                           41 SEYON STREET, BUILDING 1
                                WALTHAM, MA 02453
                       SOLICITED BY THE BOARD OF DIRECTORS
                     FOR THE ANNUAL MEETING OF STOCKHOLDERS

      The undersigned hereby appoints Walter C. Herlihy and Daniel P. Witt, and
each of them alone, proxies with full power of substitution, to vote all shares
of common stock of the Corporation which the undersigned is entitled to vote at
the Annual Meeting of Stockholders of Repligen Corporation to be held on the
10th day, September, 2003 at 10:00 a.m., local time, at the offices of the
Corporation, 41 Seyon Street, Waltham, Massachusetts 02453, and any adjournments
thereof, upon matters set forth in the Notice of Annual Meeting of Stockholders
and Proxy Statement dated July _, 2003, a copy of which has been received by the
undersigned. The proxies are further authorized to vote, in their discretion,
upon such other business as they may be incidental to the meeting or any
adjournments thereof.

                (Continued and to be signed on the reverse side)

SEE REVERSE SIDE                                                SEE REVERSE SIDE
                                                                14475



                        ANNUAL MEETING OF STOCKHOLDERS OF
                              REPLIGEN CORPORATION
                               September 10, 2003
                           Please date, sign and mail
                             your proxy card in the
                            envelope provided as soon
                                  as possible.

     Please detach along perforated line and mail in the envelope provided.

   PLEASE SIGN, DATE AND RETURN PROMPTLY IN THE ENCLOSED ENVELOPE. PLEASE MARK
                  YOUR VOTE IN BLUE OR BLACK INK AS SHOWN HERE.

1. To elect a Board of Directors for the ensuing year;

NOMINEES:
O Robert J. Hennessey   O Walter C. Herlihy, Ph.D.
O G. William Miller     O Alexander Rich, M.D.
                        O Paul Schimmel, Ph.D

FOR ALL NOMINEES        WITHOLD AUTHORITY FOR ALL NOMINEES     FOR ALL EXCEPT
                                                               See instructions
                                                               below
|_|                                  |_|                             |_|

INSTRUCTION: To withhold authority to vote for any individual nominee(s), mark
"FOR ALL EXCEPT" and fill in the circle next to each nominee you wish to
withhold, as shown here:

2. To consider and act upon a proposal to increase the size of the Board of
Directors to eight members;

For                Against              Abstain
|_|                  |_|                  |_|

3 To elect Thomas F. Ryan, Jr. to fill one of the vacancies on the Board of
Directors, if Proposal 2 is approved by the Stockholders;

For                Against              Abstain
|_|                  |_|                  |_|

4 To consider and act upon a proposal to amend the Company's bylaws to allow the
Board of Directors to set the size of the Company's Board of Directors and to
appoint Directors to fill any vacancy until the next Annual Meeting;

For                Against              Abstain
|_|                  |_|                  |_|

5. To consider and act upon a proposal to amend the 2001 Repligen Corporation
Stock Option Plan, to increase both the number of options the Company
automatically grants per year and the aggregate number of options granted to its
non-employee directors;

For                Against              Abstain
|_|                  |_|                  |_|

6. To consider and act upon a proposal to amend and restate the 2001 Repligen
Corporation Stock Option Plan, to allow shares of restricted stock to be awarded
under such plan;

For                Against              Abstain
|_|                  |_|                  |_|

7. To ratify the selection of Ernst & Young LLP as the independent auditors of
Repligen for the fiscal year ending March 31, 2004; and

For                Against              Abstain
|_|                  |_|                  |_|



8. In their discretion, the proxies are authorized to vote upon such other
matters as may properly come before the meeting or any adjournment thereof.

THE SHARES REPRESENTED BY THIS PROXY WILL BE VOTED AS DIRECTED OR, IF NO
DIRECTION IS GIVEN, WILL BE VOTED FOR THE ELECTION OF DIRECTORS AND FOR THE
PROPOSALS IN ITEMS 2, 3, 4, 6 AND 7 AND AUTHORITY WILL BE DEEMED GRANTED UNDER
ITEM 8 TO HAVE THE PROXIES VOTED UPON SUCH ADJOURNMENTS OR POSTPONEMENTS
THEREOF.

To change the address on your account, please check the box at right and
indicate your new address in the address space above. Please note that changes
to the registered name(s) on the account may not be submitted via this method.

  Signature of Shareholder Date:                  Signature of Shareholder Date:

      Note: Please sign exactly as your name or names appear on this Proxy. When
shares are held jointly, each holder should sign. When signing as executor,
administrator, attorney, trustee or guardian, please give full title as such. If
the signer is a corporation, please sign full corporate name by duly authorized
officer, giving full title as such. If signer is a partnership, please sign in
partnership name by authorized person.



                        ANNUAL MEETING OF STOCKHOLDERS OF
                              REPLIGEN CORPORATION
                               September 10, 2003
                            PROXY VOTING INSTRUCTIONS

MAIL - Date, sign and mail your proxy card in the envelope provided as soon as
possible.

                                     - OR -

TELEPHONE - Call toll-free 1-800-PROXIES from any touch-tone telephone and
follow the instructions. Have your control number and proxy card available when
you call.

                                     - OR -

INTERNET - Access "www.voteproxy.com" and follow the on-screen instructions.
Have your control number available when you access the web page.

COMPANY NUMBER
ACCOUNT NUMBER
CONTROL NUMBER

--------------------------------------------------------------------------------
Please detach along perforated line and mail in the envelope provided IF you are
not voting via telephone or the Internet.

--------------------------------------------------------------------------------
1. To elect a Board of Directors for the ensuing year;

NOMINEES:

O Robert J. Hennessey    O Walter C. Herlihy, Ph.D.
O G. William Miller      O Alexander Rich, M.D.
                         O Paul Schimmel, Ph.D

FOR ALL NOMINEES         WITHOLD AUTHORITY FOR ALL NOMINEES     FOR ALL EXCEPT
                                                                See instructions
                                                                below

|_|                                  |_|                             |_|

INSTRUCTION: To withhold authority to vote for any individual nominee(s), mark
"FOR ALL EXCEPT" and fill in the circle next to each nominee you wish to
withhold, as shown here:

2. To consider and act upon a proposal to increase the size of the Board of
Directors to eight members;

For                Against              Abstain
|_|                  |_|                  |_|

3 To elect Thomas F. Ryan, Jr. to fill one of the vacancies on the Board of
Directors, if Proposal 2 is approved by the Stockholders;

For                Against              Abstain
|_|                  |_|                  |_|

4 To consider and act upon a proposal to amend the Company's bylaws to allow the
Board of Directors to set the size of the Company's Board of Directors and to
appoint Directors to fill any vacancy until the next Annual Meeting;

For                Against              Abstain
|_|                  |_|                  |_|

5. To consider and act upon a proposal to amend the 2001 Repligen Corporation
Stock Option Plan, to increase both the number of options the Company
automatically grants per year and the aggregate number of options granted to its
non-employee directors;

For                Against              Abstain
|_|                  |_|                  |_|



6. To consider and act upon a proposal to amend and restate the 2001 Repligen
Corporation Stock Option Plan, to allow shares of restricted stock to be awarded
under such plan;

For                Against              Abstain
|_|                  |_|                  |_|

7. To ratify the selection of Ernst & Young LLP as the independent auditors of
Repligen for the fiscal year ending March 31, 2004; and

For                Against              Abstain
|_|                  |_|                  |_|

8. In their discretion, the proxies are authorized to vote upon such other
matters as may properly come before the meeting or any adjournment thereof.

THE SHARES REPRESENTED BY THIS PROXY WILL BE VOTED AS DIRECTED OR, IF NO
DIRECTION IS GIVEN, WILL BE VOTED FOR THE ELECTION OF DIRECTORS AND FOR THE
PROPOSALS IN ITEMS 2, 3, 4, 6 AND 7 AND AUTHORITY WILL BE DEEMED GRANTED UNDER
ITEM 8 TO HAVE THE PROXIES VOTED UPON SUCH ADJOURNMENTS OR POSTPONEMENTS
THEREOF.

To change the address on your account, please check the box at right and
indicate your new address in the address space above. Please note that changes
to the registered name(s) on the account may not be submitted via this method.

  Signature of Shareholder Date:                  Signature of Shareholder Date:

      Note: Please sign exactly as your name or names appear on this Proxy. When
shares are held jointly, each holder should sign. When signing as executor,
administrator, attorney, trustee or guardian, please give full title as such. If
the signer is a corporation, please sign full corporate name by duly authorized
officer, giving full title as such. If signer is a partnership, please sign in
partnership name by authorized person.