Exhibit 99.1

                            [Letterhead of RepliGen]

FOR IMMEDIATE RELEASE
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CONTACT:

Walter C. Herlihy, Ph.D.                    David Walsey
President and Chief Executive Officer       Noonan Russo Presence Euro RSCG
(781) 250-0111, ext. 2000                   (212) 845-4257

                     Repligen Adopts Shareholder Rights Plan

WALTHAM, MA - March 4, 2003 - Repligen Corporation (Nasdaq: RGEN) today
announced that on March 3, 2003 its Board of Directors adopted a shareholder
rights plan under which all Common shareholders of record as of March 17, 2003
will receive rights to purchase shares of a new series of Preferred Stock. The
adoption of the Rights Plan is intended as a means to guard against coercive
takeover tactics and is not in response to any particular proposal.

"The implementation of a shareholder rights plan will enable the Board of
Directors, on behalf of its shareholders, to maximize long-term shareholder
value by providing a vehicle in which the Board is actively involved in
negotiating any potential takeover situations," explained Walter C. Herlihy, the
Company's President and CEO. "The time and flexibility provided by a rights plan
is essential to obtaining the best potential return for shareholders."

The rights will be distributed as a non-taxable dividend and will expire ten
years from the adoption date. Subject to certain exceptions, the rights will be
exercisable only if a person or group acquires 15 percent or more of Repligen's
outstanding Common Stock (20 percent in the case of a Grandfathered Stockholder)
or announces a tender or exchange offer upon the consummation of which such
person or group would own 15 percent or more of Repligen's outstanding Common
Stock. Each right will initially entitle Common shareholders to purchase a
fractional share of Preferred Stock for $50. Subject to certain exceptions, if
any person or group acquires 15 percent or more of Repligen's Common Stock, all
rights holders, except the acquiring person or group, will be entitled to
acquire Repligen's Common Stock (and in certain instances the stock of the
acquirer) at a discount.

The effect will be to discourage acquisitions of more than 15 percent of
Repligen's outstanding Common Stock without negotiations with the Board of
Directors. The rights will trade with Repligen's Common Stock, unless and until
they are separated upon the occurrence of certain future events. Generally,
Repligen's Board of Directors may amend the Rights Plan or redeem the rights
prior to 10 days (subject to extension) following a public announcement that a
person or group has acquired 15 percent or more of Repligen's outstanding Common
Stock. Additional details regarding the Rights Plan will be outlined in a
summary to be mailed to all shareholders following the record date.

                                     -more-


Repligen Adopts Shareholder Rights Plan, March 4, 2003
Page 2

About Repligen Corporation

Repligen Corporation is a biopharmaceutical company committed to being the
leader in the development of new drugs for pediatric developmental disorders
including autism, immune and metabolic disorders. Repligen has a Specialty
Pharmaceuticals business comprised of rProtein A(TM) and SecreFlo(TM), the
profits from which will be used to support the development of our proprietary
products. rProtein A(TM) is a consumable reagent used by the pharmaceutical
industry to produce a class of drugs called monoclonal antibodies and
SecreFlo(TM), secretin for injection, is marketed to gastroenterologists for
pancreatic assessment and for use during a gastrointestinal procedure called
ERCP. 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 21E of the Securities Exchange Act of 1934.
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 and product 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 market acceptance of our products, our ability to compete
with larger, better financed pharmaceutical and biotechnology companies, new
approaches to the treatment of our targeted diseases, our expectation of
incurring continued losses, our uncertainty of product revenues and profits, our
ability to generate future revenues, our ability to raise additional capital to
continue our drug development programs, the success of our clinical trials, 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 litigation regarding our intellectual
property rights, our limited sales and manufacturing capabilities, our
dependence on third-party manufacturers and value added resellers, our ability
to hire and retain skilled personnel, our volatile stock price, 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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