Pigs were submitted to hemorrhagic shock with and without prefeeding with a predigested elemental diet and with and without pyloric ligation. It was found that prefeeding with the predigested elemental diet protected the gastric mucosa from the stress ulcers that occurred in nine of ten of the controls. Important clinical implications can be inferred from this observation. Ligation of the pylorus in six pigs did not protect against stress ulcers in five. The effect of regurgitation of small bowel contents on generation of stress ulcers must be less in the pig than in the dog.