Enzon Allowed Significant U.S. Patent On Its PEG-Pro Drug Technology.

PISCATAWAY, N.J.--(BUSINESS WIRE)--June 10, 1998--Enzon, Inc. (NASDAQ:ENZN) announced today receipt of a Notice of Allowance from the U.S. Patent and Trademark Office for a patent on its newest generation of polyethylene glycol ("PEG") technology: Pro Drug/Transport technology. This third generation of PEG technology provides increased solubility and other drug delivery enhancements to small molecule therapeutics. The patent will broadly cover PEG-modified small molecules, such as anti-cancer, anti-fungal, antibiotic and other compounds.

The key feature of the claimed invention is the linker joining PEG to the therapeutic compound, which controls the rate of release of the compound in vivo to potentially increase its efficacy and reduce its toxicity.

This new Pro Drug/Transport technology makes it possible to "pegylate" small molecules, which has not been commercially feasible with earlier generations of PEG technology. Many small molecules have known therapeutic efficacy, but also have delivery problems. One well known example is camptothecin, a topoisomerase I inhibitor. Camptothecin has been known as an effective anti-cancer agent for some time, but has been difficult to deliver without serious side effects. While there are camptothecin analogs on the market, as well as other derivative products in clinical trials, there is significant room for improvement in the efficacy of these products. Enzon is developing PROTHECAN(tm), a Pro Drug/Transport version of camptothecin. Enzon's pre-clinical results with PROTHECAN suggest superior efficacy in animal models of human cancers when compared to the products currently on the market.

Enzon intends to file an Investigational New Drug Application for PROTHECAN during the third calendar quarter of 1998.

"We are very excited about this new patent because it represents a significant expansion of Enzon's proprietary coverage of PEG drug delivery technology as applied to small molecules," stated Peter G. Tombros, Enzon's president and chief executive officer. "Up to now we have focused primarily on proteins. This new technology will enable us to improve delivery of high potential small molecules such as antibiotics, anti-fungals and anti-cancer compounds which are typically used to treat large patient populations."

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. Enzon's research activities are focused primarily in the area of oncology. Enzon develops and markets products on its own and through strategic alliances, such as Alexion Pharmaceuticals, Inc., Baxter Healthcare Corporation, Bristol-Myers Squibb Company, Eli Lilly & Company, Rhone-Poulenc Rorer Pharmaceuticals, Inc. and Schering-Plough Corporation. Headquartered in Piscataway, NJ, Enzon has two FDA approved products, as well as several products in various stages of clinical development by itself and partners.

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, including without limitation, risks in obtaining and maintaining regulatory approval for expanded indications, market acceptance of and continuing demand for Enzon's products and the impact of competitive products and pricing.

CONTACT: Dana C. Bicsko

Corporate Communications &

Investor Relations Mgr.

732-980-4577

http://www.enzon.com