Gastric acid hypersecretion and accelerated gastric emptying are commonly considered as possible determinants of duodenal ulcer, but the relative frequencies of these gastric dysfunctions have never been evaluated in a homogeneous group of patients. We studied basal and pentagastrin-stimulated gastric acid secretion and gastric emptying of a radiolabeled caloric liquid meal in 99 consecutive male patients with endoscopically proven, active, uncomplicated duodenal ulcers. Compared to matched healthy subjects, ulcer patients presented increased basal and stimulated acid secretion (P less than 0.001). Sixty-nine patients had peak acid output values above the 95% confidence limits of the control population (14.2-30.6 meq/hr). Cigarette smoking was correlated with gastric acid hypersecretion. No significant difference was found between duodenal ulcer patients and controls in mean gastric emptying times. Ulcer patients showed a greater variance of gastric acid secretion and emptying values than healthy subjects. This reflects varied gastrointestinal function among ulcer patients. No significant correlation was found between gastric acid output and gastric emptying times. These findings suggest that gastric acid hypersecretion, but not accelerated gastric emptying of liquids, play a relevant role in the pathogenesis of duodenal ulcer.