1 The isolated perfused stomach of the mouse was used to study the effect of atropine and secoverine on bethanechol-induced gastric acid secretion and gastric motility. 2 Both atropine and secoverine inhibited cholinergically induced gastric acid secretion and gastric motility. 3 Inhibition of gastric acid secretion by atropine and secoverine occurred at a similar dose-range (10'9and 2 x 10-9 M). 4 Secoverine inhibited bethanechol-induced hypermotility at doses (10-ll M and above) that were lower than those of atropine (2 x 10-9 M and above) required to produce this effect. 5 Secoverine, unlike atropine markedly inhibited gastric motility at lower doses than those which affected secretion.