Gastric acid secretion was stimulated in 21 anesthetized cats by infusion of pentagastrin for 45 min. Thirty minutes later the arterial blood pressure in two groups of the cats was lowered by bleeding to 75 mmHg for two hours, during which time one group was infused with cimetidine and the other with Ringer's solution. The tapped blood was then reinfused and normotension was maintained for two hours. In the third group the cats received pentagastrin and Ringer's solution but were kept normotensive throughout the experimental period. Blood flow was determined with the microsphere distribution technique. The volume and pH of the gastric juice were measured. In the cats with hemorrhagic hypotension, mucosal erosions developd in the corpus/fundus and antrum regions irrespective of cimetidine administration. In the normotensive cats there were few erosions. The gastric mucosal blood flow decreased markedly when the arterial pressure was lowered and returned to control levels and reinfusion of blood. The volume of gastric juice was fairly constant in the experimental period, but the concentration of H+ showed a gradual fall in the three test groups. The study showed that gastric mucosal erosions may develope in cats subjected to hemorrhagic hypotension when the stomach contains gastric acid without bile.