Low basal plasma testosterone levels with normal response to human chorionic gonadotropin (HCG) stimulation and mild hyperprolactinemia and blunted luteinizing hormone (LH) response to luteinizing-releasing hormone (LRH) stimulation were found in 10 adolescent schizophrenic boys who had been treated with chlorpromazine for more than 6 months. These findings may indicate a disturbance of the hypothalamic-pituitary-gonadal function in these patients, probably due to the prolonged administration of chlorpromazine. It remains to be established whether the decrease in basal testosterone secretion is caused directly by chlorpromazine or secondarily by the drug-induced hyperprolactinemia.