This study of the effects of long-term clomiphene administration on semen analyses of oligospermic infertile males once again points to the potential therapeutic efficacy of clomiphene in certain subjects. Although the group of 16 subjects was small, all were men with long-standing infertility that had been refractory to previous treatments such as exogenous injections of human chorionic gonadotropin and varicocelectomy; 10 of the 16 men (62.5%) showed improvement in sperm counts within 2 to 5 months of starting clomiphene. Sperm motility improved moderately when counts improved; no effects on sperm morphology were noted. Of the 10 men classified as semen responders to clomiphene, 5 (50%) were successful in impregnating their wives within 2 to 8 months of starting treatment. These results approach the therapeutic efficacy seen with clomiphene in appropriately selected females with ovulatory disturbances. We have been unable to predict or characterize the patient who might be expected to show a semen response to clomiphene by history, physical examination response to previous treatment, or changes in blood testosterone levels while taking clomiphene.