Human Genome Sciences, Inc. (Nasdaq: HGSI) today announced that, in connection with its ongoing strategic alternative review process, it had previously set a bid date of July 16, 2012 for the submission of definitive proposals to acquire all outstanding common shares of HGS. In this regard, HGS yesterday sent a letter to GlaxoSmithKline (GSK) once again inviting GSK to participate in the ongoing process according to the same procedures previously established and to provide, by no later than July 16, 2012, GSK’s final bid terms, including a response to a draft agreement which will be provided to all interested bidders. The letter specifically noted that the HGS Board of Directors has previously rejected $13.00 per share as inadequate. HGS is committed to completing its exploration of strategic alternatives in a manner that ensures that HGS stockholders have the benefit of a complete and fair process and welcomes GSK to fully participate in such process. There can be no assurance that the timing of the process will not change or that the process being conducted will result in any transaction. HGS does not intend to comment further on the process unless and until an agreement in principle or definitive agreement is signed, except as otherwise required by law. ABOUT HUMAN GENOME SCIENCES Human Genome Sciences exists to place new therapies into the hands of those battling serious disease. 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 email to email@example.com. HGS, Human Genome Sciences and BENLYSTA® are trademarks of Human Genome Sciences, Inc. Other trademarks referenced are the property of their respective owners. CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS This announcement includes statements that are forward-looking. These forward-looking statements are based on our current intentions, beliefs and expectations regarding future events. We cannot guarantee that any forward-looking statement will be accurate. Investors should realize that if underlying assumptions prove inaccurate or unknown risks or uncertainties materialize, actual results could differ materially from our expectations. Investors are, therefore, cautioned not to place undue reliance on any forward-looking statement. Any forward-looking statement speaks only as of the date of this announcement, and, except as required by law, we do not undertake to update any forward-looking statement to reflect new information, events or circumstances.