Enzon Announces Schering-Plough's PEGINTRON -TM- Approved for Treatment of Hepatitis C in European Union.

Business Editors

PISCATAWAY, NJ--(BUSINESS WIRE)--May 30, 2000

Enzon, Inc., (ENZN) announced today that Schering-Plough Corporation (NYSE: SGP) was informed that the European Union's Commission of the European Communities has granted marketing authorization to PEGINTRON(TM)(peginterferon alfa-2b) as a once-weekly monotherapy for adult patients with chronic hepatitis C. PEGINTRON is a longer-acting form of Schering-Plough's INTRON(R) A (interferon alfa-2b, recombinant) Injection, developed using proprietary Enzon PEG-technology licensed to Schering-Plough. (See Schering-Plough press release this morning for data and information related to this European approval.)

In addition to this European approval, Schering-Plough is conducting clinical trials for other therapeutic indications and seeking other marketing approvals for PEG-INTRON. Phase III clinical trials are on-going with PEG-INTRON in combination therapy with REBETOL(Ribavirin, USP) for hepatitis C. In addition, PEG-INTRON is in Phase III clinical trials for two cancer indications, malignant melanoma and chronic myelogenous leukemia, as well as in early stage trials for various solid tumors. On December 23, 1999 Schering-Plough submitted a Biologics License Application to the U.S. Food and Drug Administration seeking marketing approval in the U.S. for PEG-INTRON as a once-weekly monotherapy for the treatment of chronic hepatitis C.

"This approval is an exciting event for Enzon. Schering-Plough's rapid success with PEG-INTRON and the broad scope of their activities with the combination treatment and in other indications suggest a bright future for PEG-INTRON," stated Peter G. Tombros, Enzon's president and chief executive officer. "It is the start of what we believe will be additional submissions and subsequent approvals in other venues and for a variety of indications."

Enzon is a biopharmaceutical company developing and commercializing enhanced therapeutics for life-threatening diseases through the application of its proprietary technologies, PEG Modification or PEG and Single-Chain Antibody (SCA(r)) technology. Enzon's research activities are focused on applying its technologies to enhance performance of compounds with known therapeutic efficacy. In addition to two FDA approved products, Enzon has several products in various stages of clinical development by itself and with its partners. Enzon develops and markets products on its own and through its alliance partners, which in addition to Schering-Plough include Alexion Pharmaceuticals, Baxter Healthcare, Bristol-Myers Squibb, Eli Lilly, and Aventis S.A.

Certain statements made in this press release related to potential government approvals, market potential, commercialization and sales revenues of medical products and biologics, as well as their therapeutic applications and outcomes, are forward-looking and are made pursuant to the safe harbor provisions of the Securities Litigation Reform Act of 1995. Such statements involve risks and uncertainties, which may differ materially from those set forth in these statements. In addition, the economic, competitive, governmental, technological and other factors identified in the Company's filings with the Securities and Exchange Commission could affect such results.

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