ROCKVILLE, Maryland – December 5, 2003 – Human Genome Sciences, Inc. (Nasdaq: HGSI) confirmed today that its partner, GlaxoSmithKline, presented Phase 2 clinical trial results and discussed its development plan for 480848, a lipoprotein-associated phospholipase A2 (Lp-PLA2) inhibitor, at GlaxoSmithKline R&D review meetings held for financial analysts in London and New York. During the analyst meetings, GlaxoSmithKline disclosed that it plans to advance 480848 to Phase 3 clinical trials in 2004 and is targeting 2008 for a New Drug Application (NDA) filing with the U.S. Food and Drug Administration.

Under the terms of an agreement signed in 1993, Human Genome Sciences is entitled to receive clinical development milestone payments and royalties for compounds discovered by GlaxoSmithKline through the use of Human Genome Sciences' technology and intellectual property. Under the agreement, Human Genome Sciences will receive a milestone payment if 480848 moves into registration, and will receive royalties if the compound is commercialized. In addition, Human Genome Sciences has an option to co-promote an approved drug in the North American and European markets.

480848 will be the first genomics-derived small molecule drug arising from the Human Genome Sciences-GlaxoSmithKline collaboration to enter Phase 3 clinical development. Two other small-molecule drugs discovered by GlaxoSmithKline using Human Genome Sciences technology that have entered into clinical development are 462795 and 659032.^{1, 2} 659032, also an inhibitor of Lp-PLA2, is currently in Phase 1 clinical trials for the control and treatment of cardiovascular disease. 462795, a cathepsin K inhibitor, is currently in Phase 1 clinical trials for the treatment of patients with osteoporosis and osteoarthritis.

David Stump, M.D., Senior Vice President, Drug Development, said, "We are encouraged by the success of 480848 in Phase 2 clinical trials and by GlaxoSmithKline's decision to advance the compound into Phase 3 clinical trials. We believe that inhibition of the Lp-PLA2 enzyme ultimately may offer an important new strategy for the prevention and treatment of cardiovascular disease."

William A. Haseltine, Ph.D., Chairman and Chief Executive Officer, said, "We are very pleased that our partner, GlaxoSmithKline, plans to advance a small molecule compound arising from our collaboration into Phase 3 clinical trials. I believe that this will prove to be a classic example of the use of genomics technology for the discovery of novel drugs to prevent and treat serious illnesses."

Earlier this year, diaDexus, Inc. announced that the FDA has cleared its PLAC™ test for marketing as a diagnostic aid for use in helping predict an individual's risk for coronary heart disease. The PLAC test measures the level of lipoprotein-associated phospholipase A2 (Lp-PLA2) in human blood. The PLAC test was discovered through the use of Human Genome Sciences' technology, and Human Genome Sciences is entitled to receive royalties on sales of the PLAC test.

Human Genome Sciences is a company with the mission to treat and cure disease by bringing new gene-based drugs to patients.

HGS and Human Genome Sciences, are trademarks of Human Genome Sciences, Inc.

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 the Company's unproven business model, its dependence on new technologies, the uncertainty and timing of clinical trials, the Company's 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 planned facilities, intense competition, the uncertainty of patent and intellectual property protection, the Company's 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 Securities and Exchange Commission. 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.

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1. (HGSI Press Release) Human Genome Sciences Receives Milestone Payment From GlaxoSmithKline For Initiation Of Clinical Trials Of Second Genomics-Derived Drug For Cardiovascular Disease. February 27, 2003.
2. (HGSI Press Release) Human Genome Sciences Receives A Milestone Payment For Initiation of Clinical Trials of a Genomics-Derived Drug for Osteoporosis by GlaxoSmithKline. July 16, 2002.