The response of plasma prolactin (PRL) to oral administration of increasing doses of zinc (25.0, 37.5 and 50.0 mg) was studied in 17 normal adult men and women. Blood samples were collected at 10 and 30-min intervals over a period of 120 min after two basal times (-30 and 0 min). PRL concentrations significantly fell below basal levels in all subjects in response to the increase in plasma zinc levels, as compared to the controls. These results suggest that acute hyperzincemia can inhibit basal PRL secretion in normal individuals.