Gastric secretion was stimulated by intravenous infusion of 15 mug/kg/hr of pentagastrin before and 10 and 90 days after proximal gastric vagotomy in 16 duodenal ulcer patients. Postoperatively 15 ug/kg/hr of pentagastrin was also given in combination with 2 mug/kg/hr of carbacholine. Mean acid output in response to pentagastrin alone was reduced by 48 and 64 per cent at 10 and 90 days after the vagotomy, respectively. Mean pentagastrin-stimulated acid output and volume of gastric juice was significantly higher at 10 days than at 90 days after the operation. Mean pepsin output decreased also, but the decrease was not statistically significant. There was no significant effect of carbacholine on pentagastrin-stimulated acid output either at 10 or 90 days. Carbacholine increased pentagastrin-stimulated volume of gastric juice significantly at 10 but not 90 days postoperatively. The effect of carbacholine on pentagastrin-stimulated pepsin output was significant both 10 and 90 days after the vagotomy. Pepsin output in response to pentagastrin plus carbacholine 10 days after the operation was not significantly different from preoperative values. At 10 days postoperatively the increase in pentagastrin-stimulated volume of gastric juice by carbacholine was significantly greater than at 90 days. The corresponding differences of acid and pepsin outputs were not significant.