8-K/A

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                   ----------

                                   FORM 8-K/A

                                 CURRENT REPORT
                     PURSUANT TO SECTION 13 OR 15(d) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

         Date of report (Date of earliest event reported): June 12, 2002

                              Repligen Corporation
             (Exact Name of Registrant as Specified in its Charter)

           DELAWARE                    0-14656                 04-2729386
(State or Other Jurisdiction        (Commission            (I.R.S. Employer
      of Incorporation)             File Number)           Identification No.)

               41 Seyon Street
            Building #1, Suite 100
            Waltham, Massachusetts                          02453
   (Address of principal executive offices)               (Zip Code)

       Registrant's telephone number, including area code: (781) 250-0111

                          No change since last report.
          (Former Name or Former Address, if Changed Since Last Report)



The Registrant's Current Report on Form 8-K filed with the Securities and
Exchange Commission (the "SEC") on June 19, 2002, is hereby amended and restated
to read in its entirety as follows:

Item 4. Change in Registrant's Certifying Accountant.

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. 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 will be subject
to ratification of the stockholders at the Annual Meeting of Stockholders
scheduled for September 12, 2002.

Arthur Andersen's audit reports on Repligen's financial statements for each of
the two most recent 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 two most recent fiscal years of Repligen ended March 31,
2002 and 2001 or the interim period through June 12, 2002.

Repligen has provided Arthur Andersen with a copy of the foregoing disclosures
and has requested that Arthur Andersen furnish it with a letter addressed to the
SEC stating whether or not they agree with the above statements. A copy of this
letter, dated June 28, 2002, is filed as Exhibit 16.1 herewith.

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.

Item 7. Financial Statements, Pro Forma Financial Information and Exhibits.

      (a)   Financial Statements of Business Acquired: None required.

      (b)   Pro Forma Financial Information: None required.


      (c)   Exhibits:

      Exhibit No.       Description
      -----------       -----------

      16.1              Letter from Arthur Andersen LLP to the SEC dated June
                        28, 2002.



                                    SIGNATURE

      Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned hereunto duly authorized.

                                    REPLIGEN CORPORATION


                                    By: /s/ Walter C. Herlihy
                                    --------------------------------------------
                                    Name: Walter C. Herlihy
                                    Title: President and Chief Executive Officer

Date: June 28, 2002

EX-16.1

                                                                    Exhibit 16.1

June 28, 2002

Office of the Chief Accountant
Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C. 20549
Fax Number: (202) 942-9656

Dear Sir/Madam:

The representations made in this letter are based solely on discussions with and
representations from the engagement partner and manager on the audits of the
financial statements of this registrant for the two most recent fiscal years.
This individual is no longer with Arthur Andersen LLP.

We have read the first five paragraphs of Item 4 included in the Form 8-K/A
dated June 12, 2002 of Repligen Corporation to be filed with the Securities and
Exchange Commission and are in agreement with the statements contained therein.

Very truly yours,


/s/ Arthur Andersen LLP

Arthur Andersen LLP

cc: Barbara Burnim Day,
    Repligen Corporation