Published Zonagen Data Heralds Potential for New Contraceptive Vaccine.

Business Editors/Health & Medical Writers

THE WOODLANDS, Texas--(BW HealthWire)--September 18, 2000

Zonagen, Inc. (Nasdaq:ZONA)(PCX:ZNG) announced that data developed by Zonagen has been published in the September 2000 issue of Journal of Reproduction and Fertility indicating the potential of the Company's contraceptive vaccine. The publication reported results from two primate studies, one of which began over four years ago. These are the first studies in which a recombinant zona pellucida immunocontraceptive vaccine consistently induced infertility compared to controls in a primate model without permanent disruption of the normal menstrual cycle. This data was also presented on August 31, 2000 at The Molecular and Cellular Biology of the Egg and Embryo Extracellular Matrix Symposium held in Lake Tahoe, California.

The Company has been working on a contraceptive vaccine targeting the zona pellucida since its inception as a start-up founded by Baylor College of Medicine in 1987. Since that time Zonagen has obtained 10 issued and allowed United States patents covering the science that led to the current vaccine. The technology produces an immune response that targets the zona pellucida, the extra-cellular matrix that surrounds all mammalian eggs. This matrix is extremely complex and has been implicated in initial sperm-egg interactions. Zonagen scientists have cloned the three genes that encode for the majority of these proteins from numerous species including humans and the relevant proteins from two primate models, cynomolgus monkeys and baboons. The Company has found that active immunization against a specific zona protein confers long-term infertility, presumably by blocking sperm-egg interactions. Because of the uniqueness of the zona pellucida proteins, this infertility is not associated with any non-reproductive side effects. The most significant side effect noted in the studies is transient disruption of the normal menstrual cycle. In order to elicit this immune response, Zonagen scientists have utilized the Company's proprietary adjuvant Immumax(TM), also covered by an issued U.S. patent.

Jeffrey Harris Ph.D., Director of Molecular Biology at Zonagen and named inventor on many of the Company's zona pellucida related patents, noted, "When we first began this work there was some hope that a vaccine targeting the zona pellucida could actually be developed. This belief was held by several organizations working in the field. Over time researchers encountered serious problems, such as the inability to produce consistent immune responses against the zona pellucida as well as sorting out which zona protein to target. Adding to these issues was the concern over long-term adverse effects on the ovary. At Zonagen we have shown that active immunization against a specific zona protein leads to consistent infertility lasting over six months without permanent disruption of the normal female reproductive cycle."

Michael Holland Ph.D., Senior Principal Research Scientist in the Pest Animal Control Co-operative Research Center in Australia, stated, "Immunocontraceptive vaccines represent an important potential addition to the options available for regulating the fertility of our own and other species. For this reason a number of groups in America, Europe and Australia have been active in their development. The study of Harris and colleagues represents an important advance in realizing this goal. For the first time a comprehensive study of the contraceptive potential of all three components of the human zona pellucida has been tested alone and in combination in two primate species. This study clearly shows which is the important zona component for inducing infertility and it also shows that the contraceptive response can be reversed given sufficient time. This implies no irreversible damage was done to the ovary as some other studies in non primates have shown. As a result of this study we are one step closer to the goal of a human contraceptive vaccine."

"We are pleased with the progress that our scientists have made over the years in their efforts to develop a new contraceptive approach. It certainly has not been an easy problem to solve," said Joseph Podolski, President and CEO of Zonagen. He added, "However, we are now at a point in the vaccine's development where involvement with a large corporate entity or multinational agency is required to advance the science."

Any statements that are not historical facts contained in this release are forward-looking statements that involve risks and uncertainties, including but not limited to those relating to the uncertainties involving the Company's early stage of development, clinical trial results and FDA approval in the U.S. and approval of regulatory authorities in other jurisdictions, substantial dependence on one product, history of operating losses, future capital needs and uncertainty of additional funding, uncertainty of protection for patents and proprietary technology, litigation, governmental regulation, limited sales and marketing experience and dependence on collaborators, manufacturing uncertainties and reliance on third parties, competition and technology change, product liability and availability of insurance, and other risks identified in the Company's Annual Report on Form 10-K for the year ended December 31, 1999, as filed with the Securities and Exchange Commission.