Cell Genesys Announces Public Offering of Common Stock.

SAN FRANCISCO -- Cell Genesys, Inc. (NASDAQ:CEGE) announced today that it is selling 5,750,000 shares of its common stock pursuant to an effective shelf registration statement. Cell Genesys expects the net proceeds from the sale of the shares to be approximately $25 million after deducting fees and expenses. Cell Genesys also granted to the underwriter a 30-day option to purchase up to an additional 862,500 shares of common stock. All of the shares in the offering are being sold by Cell Genesys. Credit Suisse Securities (USA) LLC is acting as sole underwriter for the offering. Cell Genesys expects the closing of the offering to occur on or about September 13, 2006, subject to customary closing conditions.

Additional information and details with respect to the offering will be included in a final prospectus supplement and related prospectus that will be filed with the SEC prior to closing. When available, copies of the final prospectus supplement and accompanying prospectus may be obtained from Credit Suisse, Prospectus Department, One Madison Avenue, New York, New York 10010-3629 (212-325-2580).

This press release shall not constitute an offer to sell or the solicitation of an offer to buy, nor shall there be any sale of these securities in any state in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state.

About Cell Genesys

Cell Genesys is focused on the development and commercialization of novel biological therapies for patients with cancer. The company is currently pursuing two clinical stage product platforms - GVAX(R) cancer immunotherapies and oncolytic virus therapies. Ongoing clinical trials include Phase 3 trials of GVAX immunotherapy for prostate cancer, Phase 2 trials of GVAX immunotherapy for pancreatic cancer and leukemia, and a Phase 1 trial of CG0070 oncolytic virus therapy for bladder cancer. Cell Genesys continues to hold an equity interest in its former subsidiary, Ceregene, Inc., which is developing gene therapies for neurodegenerative disorders. Cell Genesys is headquartered in South San Francisco, CA and has its principal manufacturing operation in Hayward, CA. For additional information, please visit the company's website at www.cellgenesys.com.

Statements made herein about the company, other than statements of historical fact, including statements about the expected proceeds from the offering, the progress, results and timing of the company's clinical trials and preclinical programs and the nature of product pipelines are forward-looking statements and are subject to a number of uncertainties that could cause actual results to differ materially from the statements made, including risks associated with the closing of the offering, the success of clinical trials and research and development programs, the regulatory approval process for clinical trials, competitive technologies and products, patents, continuation of corporate partnerships and the need for additional financings. For information about these and other risks which may affect Cell Genesys, please see the company's Annual Report on Form 10-K for the year ended December 31, 2005 filed on March 13, 2006 and Quarterly Report on Form 10-K for the quarters ended March 31 and June 30, 2006, as well as Cell Genesys' reports on Form 8-K and other reports filed from time to time with the Securities and Exchange Commission. The company assumes no obligation to update the forward-looking information in this press release.