Serum prolactin was studied in 25 fertile and 127 infertile men. The latter included 91 oligospermic, 27 azoospermic, and 9 hypogonadotropic hypogonadal men. The mean prolactin level in all three groups of infertile men was significantly above that of the fertile group. There was no correlation among serum levels of follicle-stimulating hormone, luteinizing hormone, sperm count, and serumprolactin values. Hyperprolactinemia was found in five patients (two oligospermic, one azoospermic, and two hypogonadotropic hypogonadal men). Bromocriptine, 2.5 mg twice daily, suppressedhyperprolactinemia. In one man with hyperprolactinemic oligospermia, treatment with bromocriptineyielded significant improvement in sperm count (to normal values).