In order to elucidate the changes of the gastrointestinal hormones (GIH), glucose and/or lipid were administered orally in 54 pancreatectomized patients, 22 gastrectomized patients and 28 healthy volunteers before and after the surgery. Peripheral plasma levels of cholecystokinin (CCK), neurotensin (NT), gastric inhibitory polypeptide (GIP) and pancreatic polypeptide (PP) were measured for 180 min by radioimmunoassay specific for each CIH. Hyperresponses of CCK, NT and GIP were observed before surgery in patients with tumor of the pancreatic head. The lack of bile in the alimentary tract was confirmed as one of causative factors for the hyperresponse of NT. No significant change was observed in response of CCK, NT, CIP and PP after caudal pancreatectomy. The responses of CCK and GIP were normalized after pancreatoduodenectomy (PD) or total pancreatectomy (TP). The response of PP was decreased after PD or TP. Such change of GIP was not noted after gastrectomy. These changes of GIH after pancreatectomies were considered to be caused by surgical removal of the structures in which these GIH mainly located.