Fenoctimine is a nonanticholinergic inhibitor of gastric acid secretion in dogs and rats. Fenoctimine was more potent than cimetidine in the reduction of basal acid secretion in the gastric fistula rat and inhibited the production of gastric acid stimulated by histamine, gastrin tetrapeptide or bethanechol in the chronic gastric fistula dog. This compound is not an H2-antagonist but does inhibit the H+/K+-ATPase of hog gastric mucosa. The in vitro metabolism of fenoctimine by rat liver homogenates resulted in the oxidation of the aliphatic chain at the seven carbon, initially to an alcohol and then to a ketone. The unexpectedly weak effect of fenoctimine as a gastric antisecretory agent in humans, as well as anticholinergic effects, may be due to its extensive metabolism, which is different from that seen in dog and rat. The development of fenoctimine has been discontinued for unspecified reason.