GnRH stimulation tests were performed in 15 adult male chronic hebephrenic schizophrenics and 15 oligophrenic controls, matched for age and length of hospitalization. GnRH was given at doses of 50, 100 and 150 gamma to five subjects of each type, and FSH and LH levels in the blood were assayed at 0, 10, 20, 30, 60, and 90 minutes. The tests were performed twice in schizophrenics off therapy and after 10, 20 and 30 days of chlorpromazine therapy (4 mg/kg body weight/day, per os). The controls were not given chlorpromazine and were tested only twice. Schizophrenics showed relative increases in both FSH and LH which were greater than those of the controls, and the response persisted longer. Chlorpromazine had no effect on the test.