Human Genome Sciences Announces Adoption of Short-Term Stockholder Rights Plan

Human Genome Sciences, Inc.

announced today that its Board of Directors has adopted a Stockholder Rights Plan and declared a dividend of one share purchase right for each share of HGS's common stock held of record at the close of business on May 29, 2012. The Company's Board is committed to maximizing shareholder value through its previously announced strategic review process. The Rights Plan, which has a term of one year, is intended to allow the Company to fully engage in its strategic review process and as a means to protect the long-term interests of the Company's stockholders. The Rights Plan will not prevent any offers or transactions that the Board determines to be in the best interest of HGS and its stockholders. The Rights, which will initially trade with the Common Stock and represent the right to purchase one one-hundredth of a share of the new Series A Junior Participating Preferred Stock (the “Preferred Stock”) at $37.50 per Right, become exercisable on the tenth business day after a person or group acquires or commences a tender offer or exchange offer following the date of the Rights Plan for 15% or more of HGS's Common Stock without prior Board approval or immediately prior to the acceptance for payment of Common Stock tendered pursuant to any tender offer or exchange offer commenced by a third party prior to the date of the Rights Plan. Under the Rights Plan, ownership of HGS's Common Stock in the form of derivative securities counts towards the 15% ownership threshold. Once exercisable, the Rights permit HGS stockholders, other than the acquiror, to purchase HGS Common Stock having a market value of twice the exercise price of the Rights, in lieu of the Preferred Stock. Alternatively, when the Rights become exercisable, the Board of Directors may authorize the issuance of one share of HGS Common Stock in exchange for each Right that is then exercisable. In addition, in the event of certain business combinations, the Rights permit the purchase of the Common Stock of an acquiror at a 50% discount. Rights held by the acquiror will become null and void in each case. At any time prior to ten business days after a person or group acquires 15% of more of the Common Stock, the Rights can be redeemed for $0.01 each by action of the Board.