Human Genome Sciences Announces Proposed Public Offering of Common Stock

Human Genome Sciences, Inc. (Nasdaq: HGSI) today announced that it has commenced an underwritten public offering of up to 12,500,000 shares of its common stock. The Company intends to grant the underwriters a 30-day option to purchase up to an additional 1,875,000 shares of the Company’s common stock. The shares will be issued pursuant to a prospectus supplement filed as part of a shelf registration statement previously filed with the Securities and Exchange Commission on Form S-3.

The Company currently expects to use the net proceeds from this offering for general corporate purposes, including acquisition of additional manufacturing capacity and development of new indications for BENLYSTA™, as well as potential sales and marketing activities, clinical trial, research and development, general and administrative and manufacturing expenses and the potential retirement of debt. We may also use a portion of the proceeds for strategic investments. While we evaluate company, product, technology and similar opportunities from time to time, we currently have no material agreements or commitments with respect to any such acquisition or investment.

Goldman, Sachs & Co. and Citigroup Global Markets Inc. are acting as joint book-running managers for the offering.

This announcement shall not constitute an offer to sell or the solicitation of an offer to buy any securities of Human Genome Sciences, Inc., nor shall there be any sale of securities in any state or jurisdiction in which such an offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction. This press release is being issued pursuant to and in accordance with Rule 134 under the Securities Act of 1933, as amended. The offering will be made only by means of a prospectus, copies of which may be obtained from Goldman, Sachs & Co., at 85 Broad Street, New York, New York 10004, Attention: Prospectus Department, Toll-Free 1-866-471-2526, or by email at prospectus-ny@ny.email.gs.com and Citigroup Global Markets Inc. at Brooklyn Army Terminal, 140 58^th Street, 8^th Floor, Brooklyn, NY 11220, Attention: Prospectus Department, Toll-Free 800-831-9146.

About Human Genome Sciences

Human Genome Sciences is a commercially focused biopharmaceutical company. In the first half of 2009, HGS achieved its first product revenues when the Company delivered raxibacumab (ABthrax™) to the U.S. Strategic National Stockpile for the treatment of inhalation anthrax. HGS has two other products in late-stage clinical development: ZALBIN™ (formerly Albuferon^®) for chronic hepatitis C and BENLYSTA^TM (formerly LymphoStat-B^®) for systemic lupus erythematosus.

For more information about HGS, please visit the Company’s web site at www.hgsi.com. Health professionals and patients interested in clinical trials of HGS products may inquire via e-mail to medinfo@hgsi.com or by calling HGS at (877) 822-8472.

HGS, Human Genome Sciences, ABthrax, Albuferon, BENLYSTA, and ZALBIN are trademarks of Human Genome Sciences, Inc.

Safe Harbor Statement

This announcement contains forward-looking statements within the meaning 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 are based on Human Genome Sciences’ current intent, belief and expectations. These statements are not guarantees of future performance and are subject to certain risks and uncertainties that are difficult to predict. Actual results may differ materially from these forward-looking statements because of Human Genome Sciences’ unproven business model, its dependence on new technologies, the uncertainty and timing of clinical trials, Human Genome Sciences’ ability to develop and commercialize products, its dependence on collaborators for services and revenue, its substantial indebtedness and lease obligations, its changing requirements and costs associated with facilities, intense competition, the uncertainty of patent and intellectual property protection, Human Genome Sciences’ dependence on key management and key suppliers, the uncertainty of regulation of products, the impact of future alliances or transactions and other risks described in the Company’s filings with the SEC. Existing and prospective investors are cautioned not to place undue reliance on these forward-looking statements, which speak only as of today’s date. Human Genome Sciences undertakes no obligation to update or revise the information contained in this announcement whether as a result of new information, future events or circumstances or otherwise.