The heat probe is a recently developed instrument for endoscopic treatment of bleeding. A prototype probe was used in 16 patients with significant hemorrhage from peptic ulcers (10 duodenal and six gastric). It proved impossible to treat four of the patients with duodenal ulcers because of obscuring clots or active bleeding. Rebleeding occurred in only one of 12 patients who had undergone successful application of the probe and ceased after a second treatment. There were no complications due to treatment.