Background/Aims: A clear therapeutic regimen for the optimal treatment of Helicobacter pylori (H. pylori) infection has not emerged. We evaluated the eradication rate and side effects of triple regimen with low-dose clarithromycin (0.5 g/day). Methods: One hundred and one patients with duodenal ulcer (n=72), gastric ulcer (n=19), or combined duodenal and gastric ulcer (n=10) were enrolled. H. pylori infection was assessed by histology and rapid urease test before therapy and 4-6 weeks after finishing the treatment of triple regimen. Patients were treated either with omeprazole 20 mg b.d., amoxicillin 1.0 g b.d. and clarithromycin 250 mg b.d. (OAC; n=66) or with omeprazole 20 mg b.d., metronidazole 500 mg b.d. and clarithromycin 250 mg b.d. (OMC; n=35) for 2 weeks. Follow-up endoscopy was performed on 60 patients (OAC; n=41, OMC; n=19). Side effects were evaluated after completion of therapy. Results: Eradication rate of OAC group was 85.4% and that of OMC group was 78.9%. Side effects were observed in 18.2% of the OAC group and 17.1% of the OMC group. Conclusions: Both triple regimens have low rates of side effects. OAC regimen with low-dose clarithromycin shows slightly higher eradication rate of H. pylori than OMC regimen. (Kor J Gastroenterol 1999;34:35 - 41)