BACKGROUND: The role of medical treatment for patients with bleeding peptic ulcers is uncertain. METHODS: We conducted a double-blind, placebo-controlled trial in 220 patients with duodenal, gastric, or stomal ulcers and signs of recent bleeding, as confirmed by endoscopy. In 26 patients the ulcers showed arterial spurting, in 34 there was active oozing, in 35 there were nonbleeding, visible vessels, and in 125 there were adherent clots. The patients were randomly assigned to receive omeprazole (40 mg given orally every 12 hours for five days) or placebo. The outcome measures studied were further bleeding, surgery, and death. RESULTS: Twelve of the 110 patients treated with omeprazole (10.9 percent) had continued bleeding or further bleeding, as compared with 40 of the 110 patients who received placebo (36.4 percent) (P<0.001). Eight patients in the omeprazole group and 26 in the placebo group required surgery to control their bleeding (P<0.001). Two patients in the omeprazole group and six in the placebo group died. Thirty-two patients in the omeprazole group (29.1 percent) and 78 in the placebo group (70.9 percent) received transfusions (P<0.001). A subgroup analysis showed that omeprazole was associated with significant reductions in recurrent bleeding and surgery in patients with nonbleeding, visible vessels or adherent clots, but not in those with arterial spurting or oozing. CONCLUSIONS: In patients with bleeding peptic ulcers and signs of recent bleeding, treatment with omeprazole decreases the rate of further bleeding and the need for surgery.