The role of bile in the pathogenesis of chronic gastric ulcer was studied in 10 grown-up miniature pigs. After an observation period of 14-186 days, 4 pigs out of $ with total diversion of bile into the stomach developed peptic ulcers in the glandular part of the stomach, whereas none of 5 sham operated pigs developed ulcers after an observation period of 150-196 days. This difference was significant (p <0.05). In all 5 pigs with bile diversion the pyloric gland area enlarged at the cost of the fundic gland area, whereas this was not the case in the 5 controls. This difference was also significant (p (0.01). There was no significant change in gastric emptying after the operations. It is concluded that bile can cause gastric ulcer in the pig.