Aspects of the physiology of the testis and epididymis are discussed which might be relevant to future methods of contraception in the male. These include the blood-testis barriers, both at the tubular and vascular level, testicular and scrotal thermoregulation and maturation of spermatozoa in the epididymis. Possible adverse consequences of interfering with spermatogenesis are also considered, such as reduced endocrine responsiveness of the testis, increased incidence of genetic abnormalities and abnormal development of embryos produced by sub-fertile males.