Ten schizophrenic and five epileptic patients under antipsychotic drug treatment were studied to evaluate sleep-related GH secretion. Four of the schizophrenic patients had a high secretion peak of GH (range 15.2 to 38.0 ng/ml), four had a moderate peak (range 5.8--8.3 ng/ml), while two had no increase in GH secretion during sleep (range 0.5--1.0 ng/mg). Four of the five epileptic patients had a moderately increased secretion (range 5.8--9.2 ng/ml) and one had no increase in GH secretion during sleep. Thus, the GH secretory pattern varied with the patient as in known to be also with healthy individuals. However, no clear disturbances were noted in sleep-related GH secretion in schizophrenic patients receiving antipsychotic drug treatment, when compared e.g. to non-schizophrenic, epileptic patients under a same kind of drug treatment.