It is two years since a general meeting of the Gesellschaft fur Biologische Chemie first requested us to organize the 21 st Mosbach Colloquium on mammalian reproduction, and one year since we received final authorization to do so. The present volume contains the papers read at the Colloquium, but the discussions have been omitted because writing and proof reading them would have delayed the appearance of this volume for an unjustifiable long time. Besides, in most cases the discussion was of a relatively specific nature and we did not consider it essential, bearing in mind that the purpose of...