In healthy human volunteers we evaluated the effect of a single oral dose of 1 g/kg of alcohol (12.5%, v/v) on the output of prostaglandin E2, prostaglandin F2 alpha and 6-keto-prostaglandin F1 alpha in the gastric juice. In control experiments performed at intervals of 5-8 days, the subjects received the identical volume of water. Ninety minutes after the ingestion of alcohol, or water, first the basal secretion and subsequently the secretion after injection of pentagastrin (6 micrograms/kg, i.m.) were collected over periods of 60 min. The concentrations of the three prostaglandins were determined by radio-immunoassay. After ingestion of alcohol, the volume of gastric juice in response to pentagastrin stimulation was reduced by 24.6%, as compared with the control period. Ingestion of alcohol led to a significant reduction in the concentration of prostaglandin E2 (-42.7%) after stimulation with pentagastrin. The prostaglandin E2 output per hour was markedly inhibited by the ingestion of alcohol, both in the basal period (-47%) and after stimulation with pentagastrin (-55%). While stimulation with pentagastrin did not influence the secretion of PGE2 or PGF2 alpha, the output of 6-keto-PGF1 alpha increased appreciably (+88%) after the administration of pentagastrin. Alcohol also significantly (-28%) inhibited the secretion of 6-keto-PGF1 alpha in the period following the administration of pentagastrin. It is supposed that the inhibition of the secretion of prostaglandin E2 and 6-keto-prostaglandin F1 alpha by acute alcohol ingestion, might be of significance for the development of alcohol-induced mucosal damage in the stomach.