Hyperprolactinemia associated with male infertility or impotence was found in ten patients. Mean prolactin level was 83 +/- 49 ng/ml (range 46-26- ng/ml). The etiological bases of the hyperprolactinemia were a microadenoma in one patient, liver disease in two, and idiopathic in seven patients. Bromocriptine treatment, 2.5-7.5 mg daily for 8-16 weeks lowered prolactin to normal levels in all patients. Three oligoasthenospermic subjects showed a marked increase in sperm motility; their wives conceived within 5-8 weeks of treatment after longstanding infertility. Two of these women gave birth to normal babies and one aborted in the first trimester of pregnancy. The mechanism by which hyperprolactinemia interferes with sperm production and the effect of bromocriptine on this mechanism is discussed.