The action of lei-enkephaline (EK) on gastric secretion was studied in various models: in 4 dogs with gastric fistula according to Basov, in 4 dogs with denervated ventricles according to Heidenheim, and on an isolated mucous membrane of the frog stomach. EK effect on gastrin content in the dog blood was also studied to show its significant inhibitory action on hydrochloric acid secretion in the dog stomach. It was shown that H+ isolation, both basal and EK-stimulated, by an isolated mucous membrane of the frog stomach remains unchanged. Blood gastrin level in the dog tended to dropping down under the effect of EK.