Contacts:

Sharon Tetlow diaDexus 650-246-6403 stetlow@diadexus.com

MEDAREX AND DIADEXUS FORM COLLABORATION FOR THE DEVELOPMENT OF FULLY HUMAN ANTIBODY THERAPEUTICS

Princeton, NJ and South San Francisco, CA - January 29, 2003 - PRNewswire- FirstCall/ -- Medarex, Inc. (Nasdaq: MEDX - News) and diaDexus, Inc. today announced a collaboration for the research and development of fully human antibody therapeutics. Medarex plans to use its UltiMAb Human Antibody Development System(SM) to generate antibodies to disease targets identified by diaDexus.

Under the terms of the agreement, diaDexus and Medarex expect to develop antibodies against novel lung cancer targets. The two companies intend to share the cost of research, development and commercialization as well as potential profits resulting from any products developed through this collaboration.

In addition to the joint development and commercialization agreement, diaDexus expects to use Medarex's UltiMAb(TM) technology to generate antibodies to other therapeutic targets outside the collaboration. diaDexus intends to develop and commercialize these therapeutics on its own. Medarex could receive license fees and milestone payments as well as royalties on commercial sales of any products that diaDexus develops resulting from this second agreement.

"We are delighted to partner with Medarex and gain access to their technology and expertise in fully human antibody therapeutic development," said Patrick Plewman, President and Chief Executive Officer of diaDexus. "We believe this collaboration will enable us to accelerate the transition from targets to therapeutic products jointly in lung cancer, and independently in our other cancer programs."

"This agreement provides us with the opportunity to pair diaDexus' genomically-derived targets with our UltiMAb technology for the development of new cancer therapeutics," said Donald L. Drakeman, Ph.D., President and Chief Executive Officer of Medarex.

diaDexus, a privately held biotechnology company, based in South San Francisco, California is focused on the discovery, development, and commercialization of novel, patent protected diagnostic and therapeutic products with high clinical value. diaDexus has utilized genomics and bioinformatics to identify numerous disease-associated molecular targets. For more information, please visit www.diaDexus.com.

Medarex is a biopharmaceutical company focused on the discovery and development of therapeutics to treat life-threatening and debilitating diseases. Medarex's UltiMAb Human Antibody Development System(SM) is a unique combination of human antibody technologies that Medarex believes enables the rapid creation and development of fully human antibodies for a wide range of potential disease targets for therapeutic antibody products, including products for the treatment of cancer, inflammation, autoimmune and infectious diseases. Medarex's product pipeline is based on a variety of therapeutic antibody products developed through the use of its UltiMAb(TM) technology. Medarex creates and develops fully human antibodies for itself and others, offering a full range of antibody related capabilities, including pre-clinical and clinical development supported by cGMP manufacturing services. For more information about Medarex, visit its Web site at www.medarex.com.

For Medarex: Except for the historical information presented herein, matters discussed herein may constitute forward-looking statements that are subject to certain risks and uncertainties that could cause actual results to differ materially from any future results, performance or achievements expressed or implied by such statements. Statements that are not historical facts, including statements preceded by, followed by, or that include the words "potential"; "believes"; "anticipates"; "intends"; "plans"; "expects"; "estimates"; "could"; or similar statements are forward-looking statements. Medarex disclaims, however, any intent or obligation to update these forward- looking statements. Risks and uncertainties include risks associated with product discovery and development as well as risks detailed from time to time in Medarex's public disclosure filings with the U.S. Securities and Exchange Commission (SEC), including its Annual Report on Form 10-K for the fiscal year ended December 31, 2001 and subsequent Quarterly Reports on Form 10-Q. There can be no assurance that such development efforts will succeed, that such products will receive required regulatory clearance or that, even if such regulatory clearance were received, such products would ultimately achieve commercial success. Copies of Medarex's public disclosure filings are available from its investor relations department.

Medarex®, the Medarex logo, UltiMAb(TM), and UltiMAb Human Antibody Development System(SM) are trademarks and service marks of Medarex, Inc. All rights are reserved.

Source: Medarex, Inc.