Suppression of ovarian function with the transdermally given synthetic progestin ST 1435**ST 1435 was donated by The Population Council, Inc., New York, New York. This work was undertaken as part of the Contraceptive Development Program sponsored and coordinated by the International Committee for Contraception Research of the Population Council, Inc., New York, New York. The financial support provided by the George J. Hecht Fund, The Mellon Foundation, The Rockefeller Foundation, and the United States Agency for International Development through The Population Council, Inc., New York, New York, as well as the Finnish Gynecological Association, Helsinki, Finland, is greatly acknowledged. The content of this report does not necessarily reflect the policy of any of the funding resources.