The retardation of peptic digestion at low body temperatures first observed in vitro was found to be equally striking in vivo. Small animals, if sufficiently chilled and supplied with oxygen, were protected from digestion in the stomach of larger animals. This fact was applied in treating 19 patients who had unrelenting hemorrhages from the duodenum, stomach, and esophagus. A technique was evolved for circulating a coolant through a system of tubes and balloons in the stomach. The first experiences were encouraging, particularly in nine patients who had been bleeding profusely from duodenal ulcers and who ceased to bleed on cooling without recourse to operation. This therapy is rational for situations in which the digestive activity of gastric juice may be responsible for continued erosion and hemorrhage. It should not be relied on in situations complicated by blood dyscrasias, carcinoma, and other miscellaneous disorders.