In groups of 8 patients each, the increases in pancreatic polypeptide (hPP) serum level were measured after a protein-rich test-meal; one group received an infusion of 200 IU Salmon-calcitonin for a period of 3 hour while the other group did not. Calcitonin causes a significant inhibition of both the basal and the stimulated hPP serum level. Among the patients who did not receive a calcitonin infusion, the stimulated values after 15 to 120 minutes were significantly higher than the initial values, while patients receiving calcitonin did not show a significant increase. With calcitonin, the area under the secretion curve was 43% smaller. yet, on the basis of our results, the known gastrointestinal effects of calcitonin on pancreas secretion cannot be completely explained by the observed inhibition of hPP secretion.