Cholecystokinin (CCK) is known to inhibit gastric acid secretion and gastric emptying but its physiological role in the inhibition of gastric functions is not settled. In this study performed on 16 young male subjects, gastric acid secretion and emptying rate were determined after intragastric administration of 8% peptone meal alone or in combination with intravenous infusion of graded doses of CCK-8 (5-80 pmol/kg.h) or with addition of vegetable oil to meal without or with pretreatment with loxiglumide, a specific CCK antagonist. CCK-8 infusion at lower dose (5 pmol/kg.h) was ineffective but at higher doses (20-80 pmol/kg.h) it resulted in a significant reduction in acid output by 39 and 43% and a decrease in gastric emptying from 54% to 40 and 22%, respectively. Pretreatment with loxiglumide abolished almost completely the inhibition of both gastric acid and gastric emptying by CCK-8. Fat added to peptone meal reduced gastric acid secretion by 42-65% and decreased gastric emptying to 24-32%. The pretreatment with loxiglumide tended to reduce fat-induced inhibition of gastric acid secretion and gastric emptying but the difference in the inhibition of gastric functions between the tests without and with loxiglumide was not significant. This study provides evidence that exogenous CCK administered at pharmacological doses is a potent inhibitor of gastric acid secretion and gastric emptying and probably acts via specific CCK receptors. In contrast, fat induces inhibition of gastric acid secretion and gastric emptying that cannot be fully attributed to hormonally acting CCK.