In a prospective study designed to assess the effect of duration of antibiotic therapy on the helicobactericidal and ulcer healing efficacy of bismuth therapy, groups of patients, 10 in each group, with H. pylori-positive duodenal ulcer received a triple therapy regimen consisting of colloidal bismuth subcitrate 120 mg 4 times daily for 28 days with metronidazole 400 mg 3 times daily and tetracycline 500 mg 3 times daily for the first 3, 5 or 7 days of therapy. H. pylori infection was assessed by urease test, culture and histology performed before and 4 or more weeks after completion of therapy. Three patients (30 per cent) were H. pylori-negative after therapy in the 3 day compared with 5 (50 per cent) in the 5 day and 9 (90 per cent) in the 7 day treatment groups (3 vs 7, P = 0.01; 5 vs 7, P = 0.14). Healed ulcers were seen in 7 (70 per cent) of the 3 day, in 6 (60 per cent) of the 5 day, and in 10 (100 per cent) of the 7 day treatment groups (5 vs 7, P = 0.04). Bismuth triple therapy incorporating metronidazole and tetracycline for 7 days is associated with superior H. pylori eradication and ulcer healing rates than bismuth triple incorporating antibiotics for 3 or 5 days.