Cephalon, Inc. has announced that its wholly-owned
subsidiary, Cephalon CXS Holdings Pty Ltd (Cephalon), has lodged the offer document
(Bidder’s Statement) for its A$0.70 a share offer for ChemGenex Pharmaceuticals
Limited (ASX: CXS) (ChemGenex) with the Australian Securities and Investments
Commission.

Cephalon is offering a 58 percent premium to the one-month
volume weighted average price of ChemGenex up to March 29, 2011, and a 59 percent
premium to the closing price on March 24, 2011, the last trading day prior to
the announcement of Cephalon’s offer. The offer is unanimously recommended by
ChemGenex’s directors in the absence of a superior proposal.

“The addition of ChemGenex’s compounds supports our
commitment to building a world-class pipeline that delivers first-in-class
therapies to patients suffering from serious, often life-threatening medical conditions,”
said Kevin Buchi, Chief Executive Officer at Cephalon.