Coulter Pharmaceutical Reacquires Rights to Bexxar Outside of the U.S. from SmithKline Beecham; The Companies Expand Collaboration in the U.S.

Business Editors/Health & Medical Writers

SOUTH SAN FRANCISCO, Calif. and PHILADELPHIA--(BW HealthWire) --April 25, 2000

Coulter Pharmaceutical (Nasdaq:CLTR) and SmithKline Beecham (NYSE:SBH) today announced an amendment to their collaboration for Bexxar(TM) (tositumomab, iodine I 131 tositumomab), Coulter's lead investigational cancer product, to allow Coulter to reacquire rights to the therapy outside of the United States. The companies have also announced an expansion of the collaboration between the two companies through a co-promotion agreement that will temporarily use Coulter's sales force for the U.S. promotion of SmithKline Beecham's (SB) oncology products, Hycamtin(R) and Kytril(R).

Under the amended agreement, Coulter will reaquire rights outside of the U.S. for the development and commercialization of Bexxar. As part of the reacquisition which will be effective on June 30, 2000, the companies have modified their existing agreement for Bexxar. Coulter intends to directly market Bexxar in Europe upon approval to specialized centers and may seek partners as appropriate in specific countries. Coulter continues to retain all rights in Japan.

"SmithKline Beecham's reassessment of Bexxar outside of the U.S. has created an opportunity for us to reacquire these rights," said Michael F. Bigham, president and chief executive officer of Coulter. "We believe that the concentrated nature of the European market for Bexxar(TM) represents an exciting opportunity for us to drive growth in the future with full profit ownership rather than a royalty participation. SmithKline Beecham continues to contribute significantly to the U.S. development and potential commercialization of Bexxar."

Kevin Lokay, vice president and director of Oncology at SmithKline Beecham, said, "We remain firmly committed to the commercialization of Bexxar in the U.S. We are excited about the commercial opportunity in this territory and believe Bexxar will help us reach our strategic goal of expanding our oncology franchise in the U.S."

The collaboration in the U.S. has been expanded to include a co-promotion agreement wherein Coulter's sales organization will assist SB's oncology sales and marketing team with the promotion of Hycamtin and Kytril for a period of time prior to the commercial launch of Bexxar. Bexxar is a radioimmunotherapy being jointly developed by Coulter and SmithKline Beecham for the treatment of relapsed and refractory, low-grade and transformed low-grade B-cell non-Hodgkin's lymphoma. Bexxar is not yet approved. The co-promotion provides an opportunity for the two sales forces to work closely together prior to the launch of Bexxar. SB will compensate Coulter for the time and efforts of its sales force in the promotion of Hycamtin and Kytril.

Michael F. Bigham said, "We are pleased to enter into this co-promotion agreement. By enabling enhanced cooperation between the Coulter and SB Oncology sales teams, we gain substantial experience working together in advance of anticipated marketing approval of Bexxar."

Coulter Pharmaceutical, Inc. is engaged in the development of novel drugs and therapies for the treatment of cancer and autoimmune diseases. The company currently is developing a family of therapeutics based upon two drug development programs: therapeutic antibodies and targeted oncologics. The company's most advanced product candidate is Bexxar(TM), a monoclonal antibody conjugated to a radioisotope. The company's therapeutic antibodies program also includes an interferon receptor antagonist. Initial efforts in the targeted oncologics program are based on tumor activated prodrug (TAP) and tumor-specific targeting (TST) technologies. For more company information, visit Coulter Pharmaceutical's web site at http://www.coulterpharm.com.

SmithKline Beecham -- one of the world's leading health care companies -- discovers, develops, manufactures and markets pharmaceuticals, vaccines, over-the-counter medicines and health-related consumer products. For company information, visit SmithKline Beecham on the World Wide Web at http://www.sb.com.

SmithKline Beecham Oncology is committed to the research, development, manufacturing and marketing of therapeutic and supportive care products in oncology. Currently, SB Oncology markets Hycamtin(R) (topotecan hydrochloride), Kytril(R) (granisetron hydrochloride) and Compazine(R) (prochlorperazine), and has novel agents in development.

Except for the historical information contained herein, the matters discussed in this news release are forward-looking statements for Coulter Pharmaceutical, Inc. that involve risks and uncertainties, including uncertainties related to product development, uncertainties related to the need for regulatory and other government approvals, dependence on proprietary technology, uncertainty of market acceptance of Bexxar(TM) or the company's other product candidates and other risks detailed from time to time in the company's filings with the Securities and Exchange Commission (SEC). In particular, see "Risk Factors" in the company's filed Form 10-K for the year ended December 31, 1999.

Under the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995, SmithKline Beecham cautions investors that any forward-looking statements or projections made by the company, including those made in this news release, are subject to risks and uncertainties that may cause actual results to differ materially from those projected. Factors that may affect the company's operations are discussed in Exhibit 99 to the company's Annual Report on Form 20-F for 1998, filed with the U.S. Securities and Exchange Commission.