Enzon Announces FDA Approval of Schering-Plough's Supplemental NDA to Market REBETOL - ribavirin, USP - Capsules Separately for Use in Combination Therapy With INTRON A for Chronic Hepatitis C.

Business & Health Editors

PISCATAWAY, N.J--(BUSINESS WIRE)--July 26, 2001

Enzon, Inc. (NASDAQ: ENZN) announced today that Schering-Plough Corporation (NYSE:SGP) has reported that it has been granted marketing approval from the U.S. Food and Drug Administration (FDA) for REBETOL(R) (ribavirin, USP) Capsules as a separately marketed product for use only in combination with INTRON(R) A (interferon alfa-2b, recombinant) Injection for the treatment of chronic hepatitis C in patients with compensated liver disease previously untreated with alpha interferon or who have relapsed following alpha interferon therapy.

The safety and efficacy of REBETOL Capsules with interferons other than INTRON A have not been established.

REBETOL had been previously approved in the United States for this indication only as a component of REBETRON(TM) Combination Therapy, which contains REBETOL Capsules and INTRON A Injection in a single package. Schering-Plough has reported it will continue to market REBETRON Combination Therapy in the United States.

Schering-Plough expects REBETOL Capsules, available by prescription only, to be available nationwide sometime this fall.

In February 2001, Schering-Plough submitted a supplemental Biologics License Application (sBLA) to the FDA seeking marketing approval of PEG-INTRON for use in combination therapy with REBETOL for the treatment of chronic hepatitis C in patients not previously treated with interferon alpha who have compensated liver disease and are at least 18 years of age.

PEG-INTRON (peginterferon alfa-2b) is a longer-acting form of INTRON(R) A (interferon alfa-2b, recombinant) Injection that uses proprietary PEG technology developed by Enzon. Under the Company's licensing agreement with Schering-Plough, Enzon is entitled to royalties on worldwide sales of PEG-INTRON.

Enzon is a biopharmaceutical company developing advanced therapeutics for life-threatening diseases through the application of its proprietary drug delivery and targeting technologies, PEG Modification, Pro Drug/Transport technology and Single-Chain Antigen-Binding (SCA(R)) protein technology. 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, which in addition to Schering-Plough Corporation, include Alexion Pharmaceuticals, Inc., Baxter Healthcare Corporation, Bristol-Myers Squibb Company, Eli Lilly & Company, and Aventis.

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 Company's Form 10-K/A, Form 10-Q's and Form 8-Ks on file with the SEC, including without limitation, 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 www.enzon.com