In a double-blind endoscopic study of 55 patients with uncomplicated duodenal ulcers, treatment with the mucosal-protective agent, bicitropeptide (BCP-Compound), was superior to that with cimetidine (Tagamet) after 6 weeks. After the administration of bicitropeptide, 77% of ulcers had completely healed and 25% had partially healed, and after treatment with cimetidine 38% had completely healed and 38% had partially healed (chi 2 = 6,316; P < 0,025). There was no difference between the results of treatment with either drug at 12 weeks. Patients were followed up 3 months after the ulcers healed, and 44% who had been on bicitropeptide and 72% on cimetidine had active ulcers (no significant difference). Blood and urine bismuth levels were estimated before therapy, after 6 weeks of therapy, and after 3 months without therapy. Results showed that in patients taking bicitropeptide, urine bismuth levels rose significantly between 0 and 6 weeks, but decreased to pretreatment levels after 3 months without therapy. Blood bismuth levels did not change.