Atropine and an eightfold greater amount of pirenzepine inhibit pentagastrin-stimulated secretion to nearly the same extent (70-75%). Neither drug influences acid concentrations markedly (18%). Atropine and pirenzepine decrease the potassium concentration of gastric juice. By increasing electrical vagal stimulation the inhibitory effect of cimetidine decreases. In contrast, inhibition of vagally stimulated secretion by pirenzepine or by atropine averages 45%, when vagally stimulated secretion amounts to more than 50% of the pentagastrin-stimulated secretion. Thus pirenzepine inhibits gastric secretion similarly to atropine. These results support the hypothesis of a histamine and a cholinergic receptor.