The inhibition of acid and pepsin secretion by metiamide and atropine was studied in the anaesthetized Heidenhain-pouch cat. Metiamide strongly inhibited acid secretion induced by histamine, pentagastrin or carbachol. Metiamide had not effect on pepsin secretion stimulated by pentagastrin and carbachol but was effective on histamine-stimulated pepsin secretion. Atropine strongly inhibited pepsin secretion but was not as effective as metiamide in the inhibition of acid secretion. Reperfusion of the pouch with acid + salicylic acid also increased pepsin secretion. This increased pepsin output was abolished by atropine, but not by metiamide. It is postulated that (1) the peptic cell probably has only cholinergic receptors which can be additionally triggered by HCl passing the peptic cell, and (2) H2-antagonists only inhibit pepsin secretion indirectly via reduction of acid output.