Enzon Announces First Patient Dosed in Clinical Trial for ATG-Fresenius S; North American Development Program for Lung Transplantation Underway.

BRIDGEWATER, N.J. -- Enzon Pharmaceuticals, Inc. (Nasdaq: ENZN) today announced the first patient has been dosed in a clinical trial for ATG-Fresenius S for the prevention of acute organ rejection in patients receiving lung transplantation.

The clinical trial is a double-blind, multi-center, randomized study comparing two different dosing regimens of ATG-Fresenius S plus the standard post-transplant triple immunosuppressive regimen to a group treated with only the standard triple immunosuppressive regimen in patients undergoing lung transplantation. The primary clinical endpoint is defined as the occurrence of acute transplant rejection, graft loss, or death within 6 months post-transplant.

ATG-FRESENIUS S is a polyclonal antibody preparation used for T-lymphocyte suppression in organ transplant patients in order to prevent organ graft rejection. As opposed to monoclonal antibodies, the product targets a range of antigens on activated T-cells and depletes T-cells that otherwise would result in an immunologic attack on the transplanted organ leading to its rejection. For solid organ transplantation, ATG-FRESENIUS S has been shown to be very effective, typically leading to a substantial improvement of graft survival. Clinicians have demonstrated that ATG-FRESENIUS S can be administered conveniently as a single high dose just prior to the surgical procedure. Moreover, clinicians have reported positive results using ATG-FRESENIUS S for conditioning regimens and prevention of graft versus host disease in bone marrow transplantation. ATG-FRESENIUS S is currently marketed by Fresenius Biotech GmbH ("Fresenius") in over 60 countries worldwide. In June 2003, Enzon licensed the exclusive North American rights to ATG-FRESENIUS S from Fresenius.

About Enzon

Enzon Pharmaceuticals is a biopharmaceutical company dedicated to the discovery, development and commercialization of therapeutics to treat life-threatening diseases. The Company has developed or acquired a number of marketed products, including PEG-INTRON(R), marketed by Schering-Plough, and ABELCET(R), ONCASPAR(R), ADAGEN(R), and DEPOCYT(R), marketed in North America by Enzon's specialized sales force. Enzon's science-driven strategy includes an extensive drug development program that leverages the Company's macromolecular engineering technology platforms, including PEG modification and single-chain antibody (SCA(R)) technologies. Internal research and development efforts are complemented by strategic transactions that provide access to additional marketed products and promising clinical compounds. Enzon has several drug candidates in various stages of development, independently and with partners. Further information about Enzon and this press release can be found on the Company's web site at www.enzon.com.

All information in this press release is as of January 6, 2005 and the Company undertakes no duty to update this information.