I.m. injection of 100 mg of sulpiride (tranquilizer) significantly raised plasmam human prolactin (hPRL) levels in all of 7 normal subjects. The mean (.+-. SE) peak value was 78.0 .+-. 16.6 ng/ml, which was observed 30 min after the injection. Daily oral administration of sulpiride (50 mg) raised plasma hPRL levels in all 7 patients with peptic ulcer, with peak values obtained within 2 wk. Lactation (galactorrhea) occurred in 2 of these patients. Sulpiride stimulates hPRL secretion in man.