Malformations and functional disturbances of the male genitalia may be caused by teratogens. 2. A short review of the prenatal development points out the possible sites of action. 3. In animals some distinct teratogens produce typical malformation syndromo spermatogenetic cells. Cyproteronacetat, an antiandrogen, suppresses the development of the accessoric genital organs and produces an external feminisation. 4. In man, cryptorchidism, agenesis of the spermatic tracts, anorchia and hypospady are known as non-hereditary malformations. 5. The teratogenic etiology of some disturbances of the spermatogenesis is discussed.