EXHIBIT 99.1

RepliGen                                 Repligen Corporation
                                         41 Seyon Street, Building #1, Suite 100
                                         Waltham, Massachusetts 02453
                                         Telephone: 781-250-0111
                                         Telefax:   781-250-0115

FOR IMMEDIATE RELEASE
- --------------------------------------------------------------------------------
CONTACT:
Walter C. Herlihy, Ph.D.                                         David A. Walsey
President and Chief Executive Officer                            The Ruth Group
(781) 250-0111, ext. 2000                                        (646) 536-7029

              Repligen Reports Third Quarter 2004 Financial Results

WALTHAM, MA - February 11, 2004 - Repligen Corporation (NASDAQ: RGEN) today
reported results for the third quarter of fiscal year 2004 ended December 31,
2003. Total revenue for the quarter was $1,321,000 compared to total revenue of
$2,417,000 for the third quarter of fiscal year 2003. Gross profit for the
quarter was $539,000, or 41% of revenue compared to $1,276,000, or 53% of
revenue for the third quarter of fiscal year 2003. Operating expenses for the
third quarter of fiscal year 2004 were $2,766,000 compared to $2,182,000, for
the third quarter in fiscal year 2003. The net loss for the third quarter of
fiscal year 2004 was $2,127,000 or $.07 per share, compared to a net loss of
$766,000 or $.03 per share for the third quarter of fiscal year 2003. Cash and
investments as of December 31, 2003 were $25,659,000.

For the nine-month period ended December 31, 2003, total revenues were
$4,801,000 compared to $5,724,000 for the same period in fiscal 2003. For the
nine-month period ended December 31, 2003, gross profit was $2,423,000, or 50%
of revenue compared to $3,252,000, or 57% of revenue for the same period in
fiscal year 2003. Operating expenses for the nine-month period ended December
31, 2003 were $9,011,000 compared to $6,556,000 for the same period in fiscal
year 2003. For the nine-month period ended December 31, 2003, the net loss was
$6,295,000 or $.21 per share compared to $2,839,000 or $.11 per share for the
same period in fiscal year 2003.

                     Update on Product Development Programs

CTLA4-Ig

      o     The United States Patent and Trademark Office issued U.S. patent #
            6,685,941 covering the use of CTLA4-Ig for the treatment of
            rheumatoid arthritis, multiple sclerosis, systemic lupus
            erythematosis and scleroderma. Repligen owns the exclusive rights to
            this patent through license agreements with The University of
            Michigan (the University) and the United States Navy. This patent
            will remain in force until 2021 and is independent from the patents
            on CTLA4-Ig that are the subject of the lawsuit that Repligen and
            the University are prosecuting against Bristol-Myers Squibb
            (Bristol).

      o     Repligen and the University are prosecuting a lawsuit against
            Bristol for correction of inventorship of certain CTLA4 patents
            issued to Bristol. We are currently appealing the September 2003
            finding of the District Court that Repligen and the University had
            not proven that a University scientist is an inventor of the patents
            in suit. In December 2003, we filed our written brief with the
            United States Court of Appeals for the Federal Circuit concerning
            the ruling of the District Court and anticipate that Bristol will
            file its brief this quarter which will be followed by oral
            arguments.


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Repligen Reports Third Quarter 2004 Financial Results, February 11, 2004
Page 7 of 8

Secretin

      o     We are currently enrolling patients in a placebo-controlled Phase 2
            clinical trial of secretin in schizophrenia. The objective of this
            study is to determine if secretin can improve the deficits in social
            cognition common in patients with schizophrenia. This trial will
            compare the effect of twice weekly dosing of 2 different dose levels
            of secretin to a placebo over two weeks. There are approximately 2
            million people in the United States with schizophrenia.

      o     In January we announced that our Phase 3 clinical trial of secretin
            for autism failed to meet its primary endpoints. We are continuing
            to analyze the data and we expect to submit a report to the Food and
            Drug Administration (FDA) this quarter for feedback.

      o     We plan to initiate an open-label Phase 1/2 clinical trial of
            secretin in Obsessive-Compulsive Disorder (OCD) in the second half
            of this year. Pending approval by the FDA, we plan to dose patients
            twice a week using subcutaneous administration. There are 3.3
            million people in the United States with OCD.

Uridine and Therapeutic Protein A

      o     In 2003 we initiated an open-label Phase 1/2 clinical trial of
            uridine in 20 patients with bipolar disorder or major depression to
            assess the impact of uridine on the depressive symptoms associated
            with these disorders, neither of which is adequately treated with
            existing drugs. We expect to complete enrollment in this study in
            the next 3 months and plan to announce the results in mid-2004.

      o     We own a U.S. composition of matter patent on recombinant Protein A
            and have licensed a patent application from the University of
            California, San Diego for therapeutic uses of Protein A. The patent
            application is based on the discovery that Protein A targets
            specific B-cells and claims the use of Protein A in the treatment of
            various autoimmune diseases and B-cell cancers. We plan to submit an
            Investigational New Drug application to the FDA to conduct a
            clinical trial with Protein A later this year.

Specialty Pharmaceuticals

      o     In May 2003, we announced the results of a large clinical trial of
            SecreFlo(TM) in which the use of SecreFlo(TM) significantly reduced
            the incidence of pancreatitis following a gastrointestinal procedure
            called ERCP. In February 2004, we terminated the September 1999
            Licensing Agreement with ChiRhoClin, based on ChiRhoClin's failure
            to meet its obligations including to use best efforts to obtain FDA
            approval of secretin for post-ERCP pancreatitis. According to the
            terms of the Licensing Agreement, Repligen has the right to recover
            certain payments made to ChiRhoClin, totaling approximately $5
            million, from ChiRhoClin's share of royalties on future sales of
            SecreFlo(TM). Repligen retains the right to sell SecreFlo(TM) until
            such payments have been recovered.

About Repligen Corporation

Repligen Corporation is a biopharmaceutical company committed to being the
leader in the development of novel therapeutics for profound neuropsychiatric
disorders with particular emphasis on applications for children. Repligen has a
Specialty Pharmaceuticals business comprised of rProtein A(TM) and SecreFlo(TM),
the profits from which will be used to partially support the development of our
proprietary products. Repligen's corporate headquarters are located at 41 Seyon
Street, Building #1, Suite 100, Waltham, MA 02453. Additional information may be
requested from www.repligen.com.


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Repligen Reports Third Quarter 2004 Financial Results, February 11, 2004
Page 8 of 8

                             SELECTED FINANCIAL DATA

Operating Statement Data:



                                            Three Months Ended             Nine Months Ended
                                               December 31,                   December 31,
                                            2003           2002           2003           2002
                                        --------------------------------------------------------

                                                                         
Total revenue                           $ 1,321,000    $ 2,417,000    $ 4,801,000    $ 5,724,000
Cost of revenue                             782,000      1,141,000      2,378,000      2,472,000
                                        -----------    -----------    -----------    -----------
Gross profit                                539,000      1,276,000      2,423,000      3,252,000

Operating expenses:
  Research and development                1,850,000      1,363,000      5,181,000      3,845,000
  Selling, general and administrative       916,000        819,000      3,830,000      2,711,000
                                        -----------    -----------    -----------    -----------
       Total operating expenses           2,766,000      2,182,000      9,011,000      6,556,000
                                        -----------    -----------    -----------    -----------

Loss from operations                     (2,227,000)      (906,000)    (6,588,000)    (3,304,000)

Investment income                           100,000        140,000        293,000        465,000
                                        -----------    -----------    -----------    -----------

Net loss                                $(2,127,000)   $  (766,000)   $(6,295,000)   $(2,839,000)
                                        ===========    ===========    ===========    ===========

Basic and diluted net loss per share
outstanding                             $      (.07)   $      (.03)   $      (.21)   $      (.11)
                                        ===========    ===========    ===========    ===========

Weighted average number of basic and
diluted shares outstanding               29,878,000     27,316,000     29,575,000     26,979,000
                                        ===========    ===========    ===========    ===========


Balance Sheet Data:
                                             December 31, 2003    March 31, 2003
                                             -----------------    --------------
Cash and investments                            $25,659,000        $18,909,000

Total assets                                    $33,150,000        $26,793,000

Stockholders' equity                            $30,343,000        $24,550,000

This release contains forward-looking statements which are made pursuant to the
safe harbor provisions of Section 27A of the Securities Act of 1933, as amended,
and Section 21E of the Securities Exchange Act of 1934, as amended. The
forward-looking statements in this release do not constitute guarantees of
future performance. Investors are cautioned that statements in this press
release which are not strictly historical statements, including, without
limitation, statements regarding current or future financial performance,
management's strategy, plans and objectives for future operations, clinical
trials and results, litigation strategy, product research, intellectual
property, development and manufacturing plans and performance such as the
anticipated growth in target markets, including, without limitation, the market
for autoimmune disease treatment and the monoclonal antibody market and
projected growth in product sales, constitute forward-looking statements. Such
forward-looking statements are subject to a number of risks and uncertainties
that could cause actual results to differ materially from those anticipated,
including, without limitation, risks associated with: the success of current and
future collaborative relationships, the success of our clinical trials and our
ability to develop and commercialize products, our ability to obtain required
regulatory approvals, our compliance with all Food and Drug Administration
regulations, our ability to obtain, maintain and protect intellectual property
rights for our products, the risk of current and future litigation regarding our
patent and other intellectual property rights, the risk of litigation with
collaborative partners, our limited sales and marketing experience and
capabilities, our limited manufacturing capabilities and our dependence on
third-party manufacturers and value-added resellers, our ability to hire and
retain skilled personnel, the market acceptance of our products, our ability to
compete with larger, better financed pharmaceutical and biotechnology companies
that may develop new approaches to the treatment of our targeted diseases, our
history of losses and expectation of incurring continued losses, our ability to
generate future revenues, our ability to raise additional capital to continue
our drug development programs, our volatile stock price, the effects of our
anti-takeover provisions, and other risks detailed in Repligen's filings with
the Securities and Exchange Commission. Repligen assumes no obligation to update
any forward-looking information contained in this press release or with respect
to the announcements described herein.

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