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                                                                                                 March 2, 2009   Walter C. Herlihy, Ph.D. President, Chief Executive Officer and Director 41 Seyon Street, Building #1, Suite 100 Waltham, Massachusetts 02453
Re: Repligen Corporation
  Form 10-K for the Year Ended March 31, 2008   Filed June 13, 2008   File No. 000-14656

Dear Dr. Herlihy:

We have reviewed your filing and have the following comments.  In our
comments, we ask you to provide us with  information to better understand your
disclosure.  Where it requests you to revi se disclosure, the information you provide
should show us what the revised disclosure  will look like and identify the annual or
quarterly filing, as applicable, in which you intend to first include it.  If you do not
believe that revised disclosure  is necessary, explain the reason in your response.  After
reviewing the information provided, we may raise additional comments and/or request
that you amend your filing.   Please understand that the purpose of our re view process is to assist you in your
compliance with the applicable disclosure  requirements and to  enhance the overall
disclosure in your filing.  We look forward to  working with you in these respects.  We
welcome any questions you may have about our comments or on any other aspect of our review.  Feel free to call us at the telephone numbers listed at the end of this letter.

Form 10-K for year ended March 31, 2008

Item 1. Business, page 3
1. Please file as an exhibit to the Form  10-K the supply agreement between the
company and Applied Biosystems, Inc.
2. We note your discussion in this sectio n of the exclusive license agreement
between the company and the Massachuset ts Institute of Technology on page 4.
Please describe the material terms of this agreement in this section and file the

Walter C. Herlihy, Ph.D.
Repligen Corporation
March 2, 2009 Page 2
agreement as an exhibit to the Form 10-K pursuant to Item 601(b)(10) of
Regulation S-K.  Alternatively, please pr ovide us with an analysis supporting
your determination that the agreement is not material to the company.
3. We note your discussion of the exclusive license agreement between the company
and the University of Michigan on page 4, which agreement has been filed as a material contract and incorporated by re ference to your 10-K.  Please describe the
material terms of the agreement in this section of the 10-K.
4. We note your discussion of the settleme nt agreement between the company and
Bristol-Myers Squibb on pages 4, 6 and 55.  Please file this agreement as an
exhibit to the Form 10-K pursuant to Item 601(b)(10) of Regulation S-K.
 Item 5. Market for Registrant’s Common Equ ity, Related Stockholder Matters and Issuer
Purchases of Equity Securities, page 14
5. Please revise to disclose the informati on required by Item 201(e) of Regulation S-
K.

Notes to Consolidated Financial Statements

11. Scripps Agreement, page 54
6. You state that, pursuant to the company’ s license agreement with The Scripps
Research Institute, Repligen has agreed to make certain additional payments in
the event it achieves specified developmental and commercial milestones.
Notwithstanding that the company has been  granted confidential treatment for
portions of this agreement, including th e amount of specific potential milestone
payments, please disclose the aggregate pot ential milestone payments to be made
under the agreement.  Alternatively, please provide your analysis why these aggregate potential payments are not material.

Definitive Proxy Statement

Compensation Discussion and Analysis, page 18
7. We note your statements on page 18 that the Compensation Committee set total
executive officer compensation in fiscal 2008 based on the Radford Biotechnology Survey.  Please revise your discussion to identify the companies from the survey that were reviewed by the Compensation Committee and used as

Walter C. Herlihy, Ph.D.
Repligen Corporation
March 2, 2009 Page 3
a basis for the salaries paid to Repligen’s  executive officers. If the companies are
too numerous to list, please disclose the criteria for including these companies in
the Survey.
 Annual Cash Incentive Compensation, page 19

8. We note your discussion concerning the pe rformance criteria c onsidered by the
Compensation Committee in making its awards for fiscal year 2008, which was comprised of company and individual objectives.
(a) With respect to company performance objectives, your disclosure is
too general.  Please disclose th e specific targets against which
company performance was measured.  Please note that disclosure of
these specific targets is warranted unless the company believes that
competitive harm would result from such disclosure, in which case it
may omit disclosure of the specific ta rgets as long as it complies with
Instruction 4 to 402(b).  In accordance with that instruction, please supplementally explain to us your basis for keeping the individual performance target information c onfidential.  Please explain why,
based upon your specific facts and ci rcumstances, publicly releasing
this information will cause Impax competitive harm; and
(b) With respect to individual executive performance, to the extent that the
performance criteria you have listed  was subject to quantification for
purposes of the Compensation Committee’s performance evaluation, please provide the metrics used.  If not, please explain how the
Compensation Committee determined th e percentage of completion of
individual results, as described on pages 21 and 22.

Equity Compensation Plan Information, page 35

9. Please revise the equity compensation plan  table to reflect information as of
March 31, 2008, the end of the most recently completed fiscal year, rather than as
of December 31, 2007, pursuant to Item 201(d) of Regulation S-K.

*    *    *    *

Please provide us the information request ed within 10 busine ss days or tell us
when you will provide us with a response.  Please furnish a cover letter with your response that keys your responses to our  comments and provide any requested
information.  Detailed cover letters greatly facilitate our  review.  Please furnish your
letter on EDGAR under the form type label CORRESP.

Walter C. Herlihy, Ph.D.
Repligen Corporation March 2, 2009 Page 4
  We urge all persons who are responsible for the accuracy and adequacy of the
disclosure in the filing to be certain that the filing includes all in formation required under
the Securities Exchange Act of 1934 and th at they have provided all information
investors require for an informed invest ment decision.  Since the company and its
management are in possession of all facts re lating to a company’s disclosure, they are
responsible for the accuracy and adequacy of the disclosures they have made.
  In connection with responding to our co mments, please provide, in your letter, a
statement from the company acknowledging that:
• the company is responsible for the adequacy  and accuracy of the disclosure in the
filing;
• staff comments or changes to disclosure  in response to staff comments do not
foreclose the Commission from taking any action with respect to the filing; and
• the company may not assert staff comme nts as a defense in any proceeding
initiated by the Commission or any person under the federal secu rities laws of the
United States.

In addition, please be advise d that the Division of Enfo rcement has access to all
information you provide to the staff of the Divi sion of Corporation Fi nance in our review
of your filing or in response to our comment on your filing.
Please contact Laura Crotty, Staff Attorne y, at (202) 551-3563 or myself at (202)
551-3715 if you have questions regarding the pr ocessing of your res ponse as well as any
questions regarding comments and related matters.

Sincerely,

Jeff Riedler Assistant Director