In spite of the broad selection of contraceptive methods available 38% of all pregnancies are unintended worldwide and 22% end in an abortion. These facts alone clearly indicate the strong need for broadening contraceptive choices.The status of reproductive science, however, has so far led only to pharmacological fertility control measures with high standards of safety, efficacy and convenience for females. As far as men are concerned, there is still no effective reversible male contraceptive available. Nonetheless, one third of all contraceptive methods used worldwide depend on male "cooperation".With the new opportunities presented by molecular biology, there is now a realistic chance that new effective reversible methods for male fertility control can be developed. However, much more basic research is needed to reach this goal.As a consequence the Rockefeller Foundation and the Ernst Schering Research Foundation decided to take up this challenge and mounted a multi-year global collaborative effort, involving a network of top-level research institutions to intensify research on the regulation of the male reproductive system with special emphasis on post-testicular activity, using new approaches in molecular pharmacology (Application of Molecular Pharmacology of Posttesticular Activity - AMPPA - network).