Bioenvision Extends Exclusive Option to Market Clofarabine in Japan and Southeast Asia.

Business Editors/Health/Medical Writers

NEW YORK--(BUSINESS WIRE)--May 18, 2004

Bioenvision, Inc. (Amex:BIV) today announced that it has extended its exclusive, irrevocable option, subject to certain conditions, to manufacture, market and distribute clofarabine, Bioenvision's lead drug for the treatment of pediatric and adult acute leukemias, in Japan and South East Asia. Bioenvision obtained the option extension from Southern Research Institute, the inventor of clofarabine. Bioenvision is actively seeking a co-marketing partner to convert this option into a license on terms to be agreed upon between Bioenvision and Southern Research Institute.

"We continue to maintain high level dialogue with several reputable companies with expertise in the marketing of cancer drugs in Japan and Southeast Asia and we believe the extension of time to exercise the option will enhance the likelihood that we can successfully source the marketing function in this commercially valuable territory," stated Dr. Christopher B. Wood, M.D., Chairman and Chief Executive Officer of Bioenvision.

"The Asian option is one of many of our current initiatives which could have great commercial potential. Consummating a deal with one of the major Japanese pharmaceutical companies could positively and materially impact the Company's projected revenues because of the up-front and milestone payments and royalty streams which may be associated this type of transaction," added David P. Luci, Director of Finance and General Counsel of Bioenvision.

Bioenvision originally obtained the right to manufacture, market and distribute clofarabine worldwide outside of Japan and Southeast Asia pursuant to its August 1998 co-development agreement with Southern Research Institute. Bioenvision subsequently outsourced an option to develop clofarabine for human cancer applications, subject to achievement of certain milestones and certain other conditions, in the U.S. and Canada in March 2001. Bioenvision's European development program for clofarabine is on target with pivotal, Phase II, multi-centre studies ongoing in both pediatric and adult acute leukemias.

About Clofarabine

Bioenvision's partner in North America, ILEX Oncology Inc. (Nasdaq:ILXO), recently completed the New Drug Application (NDA) to the U.S. Food and Drug Administration (FDA) for clofarabine for the treatment of refractory or relapsed acute leukemia in children. Bioenvision, Inc. granted ILEX Oncology, Inc. (Nasdaq:ILXO) the right to develop clofarabine in the United States and Canada. Bioenvision is entitled to milestone payments tied to the development of the compound and is entitled to royalties on North American sales. Bioenvision is developing clofarabine exclusively in the rest of the world. Bioenvision originally obtained clofarabine development and commercialization rights under patents held by Southern Research Institute.

Clofarabine is a second-generation purine nucleoside antimetabolite. Nucleoside analogues are antimetabolites that affect DNA synthesis. Clofarabine was rationally designed to combine many of the favorable properties of the two most commonly used nucleoside analogs, fludarabine and cladribine, but is reported to have greater potency at damaging the DNA of Leukemia cells than these other agents. (Blood, "Mitochondrial Toxicity of Deoxyadenoside Analogs", November 15, 2000, Volume 96, Number 10). In a single center Phase II study of clofarabine in adult patients with refractory AML, 42% of the patients had a complete response rate (CR) and a further 13% had a partial response (CRp).

About Bioenvision

Bioenvision's (Amex:BIV) primary focus is the development and distribution of compounds and technologies for the treatment of cancer. Bioenvision has a broad pipeline of products for the treatment of cancer, including: clofarabine (in co-development with ILEX Oncology, Inc.), Modrenal(R) (for which Bioenvision has obtained regulatory approval for marketing in the United Kingdom for the treatment of post-menopausal breast cancer following relapse to initial hormone therapy), and other products in clinical trials. Bioenvision is also developing anti-infective technologies, including the OLIGON technology; an advanced biomaterial that has been incorporated into various FDA approved medical devices. For more information on Bioenvision please visit our Web site at www.bioenvision.com.

Certain statements contained herein are "forward-looking" statements (as such term is defined in the Private Securities Litigation Reform Act of 1995). Because these statements include risks and uncertainties, actual results may differ materially from those expressed or implied by such forward-looking statements. Specifically, factors that could cause actual results to differ materially from those expressed or implied by such forward-looking statements include, but are not limited to: risks associated with preclinical and clinical developments in the biopharmaceutical industry in general and in Bioenvision's compounds under development in particular; the potential failure of Bioenvision's compounds under development to prove safe and effective for treatment of disease; uncertainties inherent in the early stage of Bioenvision's compounds under development; failure to successfully implement or complete clinical trials; failure to receive marketing clearance from regulatory agencies for our compounds under development; acquisitions, divestitures, mergers, licenses or strategic initiatives that change Bioenvision's business, structure or projections; the development of competing products; uncertainties related to Bioenvision's dependence on third parties and partners; and those risks described in Bioenvision's filings with the SEC. Bioenvision disclaims any obligation to update these forward-looking statements.