BACKGROUND Successful treatment of Helicobacter pylori infection results in cure of peptic ulcer disease. Multi-drug regimens are needed to cure this infection. We studied the effectiveness and side effect profile of two antibiotics active against Helicobacter pylori, metronidazole and clarithromycin, combined with omeprazole. METHODS We evaluated a combination therapy for H. pylori infection consisting of metronidazole (500 mg b.d.), omeprazole (20 mg b.d.), and clarithromycin (250 mg b.d.) for 2 weeks, followed by ranitidine 300 mg daily for 4 weeks. RESULTS Thirty-three patients with documented H. pylori infection were studied. Twenty had previously failed antimicrobial therapy, including one with metronidazole-based triple therapy and eight with macrolide-based therapy (five with clarithromycin-based therapy), and 11 with amoxycillin, tetracycline, and bismuth. H. pylori status was determined by histopathology using the Genta stain and by culture. H. pylori status was determined at entry and 4 weeks after completing antimicrobial therapy. The H. pylori infection was cured in 88% (95% CI = 72%-96%) including 90% of those who had failed previous anti-H. pylori therapies. Mild side effects were reported by 18%. CONCLUSIONS We conclude that the combination of metronidazole, omeprazole and clarithromycin is an effective treatment for H. pylori infection.