By arranging a series of psychological contingencies (unpredictability, uncontrollability, conflict), coupled with delivery of a physical stimulus (electric shock), we produced gastroduodenal mucosal lesions in 7 of 8 rhesus monkeys. The most severe conflict paradigm most consistently produced lesions across subjects. Of the 30 lesions observed by endoscopy, 80% occurred near the anatomic junction of gastric body and antrum, in the antrum, or in the duodenum. Lesions varied in severity from discolorations of the mucosa to disruptions of mucosal integrity. Lesions in the stomach generally disappeared in several days despite the continuation of stress; some duodenal lesions were equally evanescent, but in 2 monkeys, lesions lasted over a week. Hydrogen ion kinetics were measured in 2 monkeys that developed gastric lesions and 2 that developed duodenal lesions. The rate at which hydrogen ion entered the duodenum was uniformly suppressed for all 4 monkeys during their first session of shock avoidance; during their last session, the gastric subgroup continued to show suppression while the duodenal subgroup returned towards control levels. Serum gastrin levels were unchanged by the multiple-stress procedures. Our finding of consistently producible, stress-induced gastroduodenal pathology in anatomic areas similar to those involved in man suggests that the subhuman primate is suitable for further efforts to produce an animal model of psychosomatic ulcer disease.