Gastrointestinal bleeding is a leading cause of morbidity and mortality. Rebleeding rates are low with clean ulcer bases and higher with adherent clots and visible vessels. Many endoscopists treat adherent clots hoping to reduce the incidence of rebleeding. It has been suggested that treatment with heater probe or injection may increase rebleeding compared with medical treatment. AIM: To study if treatment with injection followed with heater probe will reduce the incidence of rebleeding in patients with adherent clots. METHODS: Patients at seven centers with gastrointestinal bleeding were consented prior to endoscopy and found to have fresh adherent clots with no active bleeding. Strict criteria were used to define adherent clots. The clot was irrigated with 200 cc of forcibly injected water. Patients were then stratified for center, age, NSAID use and ulcer location, and randomized into treatment with injection and heater probe or medical management. Those randomized to endoscopic therapy had the base of the adherent clot injected with 1/10,000 adrenaline in four quadrants with at least 1 cc in each quadrant. The clot was then removed. With the heater probe set at 30 joules a minimum of 3 coaptive pulses were used until cavitation and adequate coagulation was obtained. All patients received standard medical treatment including omeprazole 20 mg bid. Patients were evaluated for rebleeding for one month. RESULTS: 56 patients were enrolled. Rebleeding rates were 34.3% (12/35) in the medical treatment arm versus 4.8% (1/21) in the endoscopic treatment arm. Data analysis using the Fisher Exact two tailed test of treatment received vs. rebleed indicated significance (p<0.02). CONCLUSIONS: This study answers the question as to whether or not to treat nonbleeding densely adherent clots. Endoscopic treatment with injection of the base of the clot, clot removal, and heater probe coagulation significantly reduces rebleeding rates in patients with peptic ulcer disease with nonbleeding densely adherent clots. Funded in part by an unrestricted grant from Astra Merck.