Ketamine exhibited effects on gastric acid secretion total acidity and acid output. Reduction of secretion by ketamine did not appe,r to be significantly different from values obtained with atropine or hexamethonium. In addition to atropine- and hexamethonium-like effects, ketamine also appeared to decrease gastric secretion through a potentiating activity on the sympathetic nervous system. When sympathetic activity was potentiated by cocaine, the antisecretory effect of ketamine appeared to be significantly reduced, compared with that of atropine. Furthermore, after alpha- or alpha- and beta-blockade, ketamine produced similar decreases in secretion, although maximum inhibitory effect was obtained after beta-blockade. Potentiation of adrenergic activity by ketamine seemed to be mediated through alpha-receptors. Histamine H2 receptors did not appear to be involved in the antisecretory action of ketamine.