Cyproterone acetate (6-chloro-17-acetoxy -1α,2α- methylene – 4,6-pregnadiene-3,20-dione) is the strongest antiandrogen known. Beside its androgenicity, this steroid has a strong progestational and thereby a partial antigonadotropic effect. There is vast evidence that the antiandrogenic effect is mainly due to competitive antagonism with androgens at the receptor sites of target organs. Experimental efforts aimed at two directions: (1) Possibilities for clinical use were evaluated and (2) cyproterone acetate was used as a tool for further investigation of testosterone-dependent events, e.g. androgen-dependent processes in the course of sexual differentiation. Almost all androgen-dependent organs and organ systems are affected by cyproterone acetate. Its most important effects in animals and humans are summarized in the following table: Since cyproterone acetate is also a potent progestagen, it could be used in combination with an estrogen as a hormonal contraceptive for women. Its antiandrogenicity would have positive effects in the so-called gestagen/androgen type of women. For use in men, only those antiandrogens would be suitable that have not only antiandrogenic but also gestagenic, hence antigonadotropic properties like cyproterone acetate. ‘Pure’ antiandrogens lacking these partial effects stimulate the secretion of gonadotropins and cause thereby enhanced synthesis and secretion of androgens which would compensate for antiandrogenic effects.