Enzon Announces the Reacquisition of ONCASPAR Commercialization Rights.

Business Editors, Health/Medical Writers

Enzon, Inc. (NASDAQ:ENZN) announced today that it has entered into an agreement with Aventis (NYSE:AVE) that provides for Enzon to reacquire its rights to market and distribute its product ONCASPAR(R) (pegaspargase).

The agreement will enable Enzon to conduct all marketing and sales activities for certain territories that had been previously licensed to Aventis, specifically the U.S., Mexico, Canada, and the Asia/Pacific region. Enzon may also seek the expansion of the current labeling of ONCASPAR through additional product development efforts.

"The acquisition of ONCASPAR allows Enzon to fund the establishment of its own sales and marketing presence in the field of oncology, a therapeutic area where our internal product development efforts have been initially focused," said Arthur J. Higgins, Enzon chairman and chief executive officer of Enzon. "This agreement is an important milestone for Enzon in our vision to become a fully integrated biopharmaceutical company."

ONCASPAR is indicated for patients with acute lymphoblastic leukemia who require L-asparaginase in their treatment regimen, but have developed hypersensitivity to native forms of L-asparaginase. During calendar 2001, Enzon reported ONCASPAR sales of approximately $9 million.

Under the agreement, Enzon will pay $15 million to Aventis as well as a 25% royalty on future net sales of ONCASPAR in the United States and Canada for a period of 12 years at which time all Enzon royalty obligations will cease.

In 1993, the Company and Aventis (formerly Rhone-Poulenc Rorer Pharmaceuticals, Inc.) entered into a license agreement for ONCASPAR and in 1994 Aventis launched the product in the U.S. Enzon has been temporarily distributing ONCASPAR since 1998 and it was expected that Aventis would resume distribution of the product during the second half of calendar 2002, at which time Enzon's revenue stream would revert back to a 27.5 percent royalty.

Enzon is a biopharmaceutical company that develops and commercializes enhanced therapeutics for life-threatening diseases through the application of its proprietary platform technologies: PEG Modification and single-chain antibodies (SCA(R)). Three products are currently marketed which utilize Enzon's technology: PEG-INTRON marketed by Schering-Plough for hepatitis C, ONCASPAR(R) for Acute Lymphoblastic Leukemia (ALL), and ADAGEN(R) a treatment for a form of Severe Combined Immunodeficiency Disease (SCID), commonly known as the "Bubble Boy Disease." In addition to three approved products, Enzon has several products in various stages of clinical development by itself and with partners, including additional indications for PEG-INTRON with Schering-Plough. A Phase III clinical trial is being conducted for PEG-INTRON for the treatment of malignant melanoma. Enzon develops and markets products on its own and through strategic alliances and licensing arrangements, which in addition to Schering-Plough Corporation, include Alexion Pharmaceuticals, Inc., Baxter HealthcareCorporation, Bristol-Myers Squibb Company, Eli Lilly & Company, Inhale Therapeutic Systems, Inc., and Micromet AG.

Except for the historical information herein, the matters discussed in this news release include forward-looking statements that may involve a number of risks and uncertainties. Actual results may vary significantly based upon a number of factors, which are described in the Enzon's Form 10-K, Form 10-Q's and Form 8-K's on file with the SEC, including without limitation, risks attendant to Enzon's limited sales and marketing experience, the risk that development efforts may be cancelled or delayed, the risk that the financial impact of the transaction may not be accretive or profitable, risks in obtaining and maintaining regulatory approval for indications and expanded indications market acceptance of and continuing demand for Enzon's products and the impact of competitive products and pricing.

This release is also available at http://www.enzon.com