Exhibit 99.1


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

FOR IMMEDIATE RELEASE
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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

    Phase 3 Study of Secretin for Autism Fails to Meet Dual Primary Endpoints
              Development of Secretin for Schizophrenia to Continue

WALTHAM, MA - January 5, 2004 - Repligen Corporation (NASDAQ: RGEN) announced
today that its Phase 3 clinical trial in autism of RG1068, synthetic human
secretin, failed to meet the study's dual primary endpoints, improvements in
social interaction as measured by the Autism Diagnostic Observation Schedule
("ADOS") and the parental Clinical Global Impression of Change ("CGI"). The
Phase 3 study had a higher placebo effect than was observed in the Phase 2 study
and neither endpoint showed a significant treatment effect in the entire group.
A prospectively defined subset analysis of the higher functioning patients
(n=68) showed a statistically significant improvement of RG1068 versus placebo
on ADOS but not on the CGI. This finding may indicate that measuring a response
to RG1068 is more difficult in patients with lower levels of cognitive function.
A preliminary review of the safety data showed no clinically meaningful
differences between RG1068 and placebo in side effects and there were no serious
adverse events observed in the Phase 3 trial.

This study was a double-blind, placebo-controlled, clinical trial which
evaluated 132 children aged 2 years 8 months to 4 years 11 months with moderate
to severe symptoms of autism. Each patient was comprehensively evaluated at
baseline, received six injections of RG1068 or a placebo over 18 weeks and was
then reevaluated for improvements in the symptoms of autism. The primary
endpoints were improvements in reciprocal social interaction as measured by
ADOS, which is performed by a trained psychologist, and the parental CGI. The
trial was carried out at 15 medical centers in the United States.

"We would like to thank the patients, their parents and the clinicians for their
participation and support in this study," stated Walter C. Herlihy, President
and Chief Executive Officer of Repligen. "We have developed an extensive
preclinical and clinical data set which supports the use of secretin in the
treatment of other neuropsychiatric diseases and we plan to continue our efforts
to develop secretin for schizophrenia. Future development in autism will be
dependent on a thorough evaluation of the Phase 3 data and discussions with the
Food and Drug Administration."

Repligen is currently conducting a Phase 2, double-blind, placebo-controlled,
clinical trial to evaluate RG1068 in patients with refractory schizophrenia.
This trial will evaluate the potential of multiple doses of RG1068 to treat the
deficits in social cognition in schizophrenia, including social interaction and
communication deficits ("negative" symptoms), which are generally resistant to
treatment with existing antipsychotic therapy. Additionally, Repligen intends to
initiate a study of RG1068 in an anxiety disorder in the second half of 2004.

                                     -more-



About Schizophrenia

Schizophrenia is a serious and chronic neuropsychiatric disorder that affects 2
million people in the United States. This devastating condition interferes with
a person's ability to think clearly, separate fantasy from reality, manage
emotions and relate to others. Patients with schizophrenia suffer from
"positive" symptoms including hallucinations, delusions, and disorganized speech
and behavior, as well as "negative" symptoms such as lack of drive and
initiative, social withdrawal and blunting of emotional expression. Deficits in
social cognition are present at all stages of the disease, contribute to the
rate of relapse and are predictive of long-term outcome. Current treatment with
antipsychotic therapy is generally directed at control of positive symptoms.
Even when successful, antipsychotic therapy has limited impact on negative
symptoms, and severe residual and incapacitating social and emotional deficits
may persist. Sales of antipsychotic drugs for schizophrenia including
Zyprexa(TM), Risperdal(TM) and Geodon(TM) totaled approximately $5 billion in
the United States in 2002. The total cost for the care and treatment of patients
with schizophrenia in the United States in 2000 was approximately $40 billion.

About Anxiety Disorders

Anxiety disorders are serious medical illnesses that affect approximately 20
million adults in the United States. These disorders include generalized anxiety
disorder, social anxiety disorder, post traumatic stress disorder, panic
disorder and obsessive-compulsive disorder. Symptoms of anxiety disorders can
significantly impact normal function including intense fear, overwhelming
anxiety and excessive embarrassment or humiliation by one's own actions.
Although conventional antidepressant and antianxiety drugs can be effective in
some patients they typically lead to adverse side effects that can include
sedation, cognitive impairment and appetite stimulation. The new biology of
secretin may provide an alternative for patients who are refractory to other
drug therapies.

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.

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, development and
manufacturing plans and performance such as the anticipated growth in 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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