About Repligen CorporationRepligen Corporation is a leading supplier of critical biologic products used to manufacture biologic drugs. Repligen also applies its expertise in biologic product development to SecreFlo™ (RG1068), a synthetic hormone being developed as a novel imaging agent for the diagnosis of a variety of pancreatic diseases. In addition, the Company has two central nervous system (CNS) rare disease programs in Phase 1 clinical trials. Repligen’s corporate headquarters are located at 41 Seyon Street, Building #1, Suite 100, Waltham, MA 02453. Important Information Concerning Proxy Materials In connection with the solicitation of proxies, on April 20, 2012, Repligen filed with the U.S. Securities and Exchange Commission (the “SEC”) a definitive proxy statement in connection with Repligen’s 2012 Annual Meeting and, in connection with the above-described agreement and the amended stockholder proposal, Repligen will file additional soliciting materials with the SEC and distribute a new proxy card (all such materials are collectively referred to as, the “Proxy Materials”). The Proxy Materials, when available, can be obtained, free of charge at the SEC’s website at www.sec.gov or from Repligen’s website at http://www.repligen.com/investor-relations/shareholder-center/ekit. STOCKHOLDERS OF REPLIGEN ARE ADVISED TO CAREFULLY READ THE PROXY MATERIALS AND ANY OTHER MATERIALS REPLIGEN FILES IN CONNECTION WITH REPLIGEN’S 2012 ANNUAL MEETING BEFORE MAKING ANY VOTING OR INVESTMENT DECISION BECAUSE THESE DOCUMENTS CONTAIN IMPORTANT INFORMATION. The Proxy Materials are available for free by writing to Repligen Corporation, 41 Seyon Street, Building #1, Suite 100, Waltham, Massachusetts 02453, Attention: Investor Relations. Safe Harbor Statement This press 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. Investors are cautioned that statements in this press release which are not strictly historical statements, including, without limitation, express or implied statements regarding Repligen’s 2012 Annual Meeting, the impact of the stockholder proposal, if approved, and other statements identified by words like “believe,” “expect,” “may,” “will,” “should,” “seek,” or “could” and similar expressions, 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: our ability to develop and commercialize products and the market acceptance of our products; reduced demand for our products that adversely impacts our future revenues, cash flows, results of operations and financial condition; our ability to obtain FDA approval of our NDA for RG1068, including the design, timing, cost and similar uncertainties related to additional clinical studies that the FDA may require for approval; whether the EMA will require additional clinical studies before approving our MAA for RG1068 and similar uncertainties regarding such additional clinical studies; our ability to obtain other required regulatory approvals; the success of current and future collaborative or supply relationships; our ability to compete with larger, better financed bioprocessing, pharmaceutical and biotechnology companies; our ability to successfully integrate Repligen Sweden AB; the success of our clinical trials; new approaches to the treatment of our targeted diseases; our compliance with all FDA and EMEA 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 capabilities; our volatile stock price; and other risks detailed in Repligen’s Annual Report on Form 10-K on file with the Securities and Exchange Commission and the other reports that Repligen periodically files with the Securities and Exchange Commission. Actual results may differ materially from those Repligen contemplated by these forward-looking statements. These forward looking statements reflect management’s current views and Repligen does not undertake to update any of these forward-looking statements to reflect a change in its views or events or circumstances that occur after the date hereof except as required by law.