Abstract: In accordance with the present invention it has been found that administration of a male sex hormone such as an androgen to a male animal perinate, particularly a male mammal neonate, suppresses subsequent masculine sexual development, particularly testicular development. Postnatal testicular growth, development of androgen secretion and circulating luteinizing and follicle stimulating hormone levels in castrated adults are all markedly diminished. This androgenic effect does not require aromatization to estrogen. Testes and adenohypophyses of treated rats are competent to respond to exogenous gonadotropins and gonadotropin releasing hormone, respectively.