GlaxoSmithKline has extended its tender offer to acquire all of the outstanding shares of Human Genome Sciences for $13.00 per share in cash to 5:00 p.m. EST on Friday, June 29, 2012. The tender offer was previously scheduled to expire at 12:00 midnight EST, at the end of the day on June 7, 2012.

Except for the extension of the tender offer expiration date, all other terms and conditions of the offer remain unchanged. As of 12:00 midnight EST at the end of the day on June 7, 2012, approximately 474,029 shares (including 24,856 shares subject to guarantees of delivery) had been tendered and not withdrawn, pursuant to the offer.

GSK’s offer represents a premium of 81% to HGS’s closing share price of $7.17 on April 18, 2012, the last trading day before HGS publicly disclosed GSK’s private offer. GSK continues to believe its offer represents full and fair value and is in the best interests of both companies' shareholders.