Aim : To assess the influence of metronidazole resistance on the efficacy of ranitidine bismuth citrate-based triple therapy regimens in two consecutive studies. Methods : In the first study, patients with a culture-proven Helicobacter pylori infection were treated with ranitidine bismuth citrate 400 mg, metronidazole 500 mg, and clarithromycin 500 mg, all twice daily for 1 week (RMC). In the second study, amoxycillin 1000 mg was substituted for clarithromycin (RMA). Susceptibility testing for metronidazole was performed with the E-test. Follow-up endoscopy was performed after ≥ 4 weeks. Antral biopsy samples were taken for histology and urease test, and culture and corpus samples for histology and culture. Results : 112 patients, 53 males, age 55 ± 14 years (39 duodenal ulcer, 7 gastric ulcer and 66 gastritis) were treated with RMC, and 89 patients, 52 males, age 58 ± 15 years (23 duodenal ulcer, 7 gastric ulcer and 59 gastritis) were treated with RMA. For RMC, intention-to-treat eradication results were 98% (59/60, 95% CI: 91–100%) and 95% (20/21, 95% CI: 76–100%) for metronidazole susceptible and resistant strains, respectively (P = 0.45). For RMA these figures were 87% (53/61, 95% CI: 76–94%) for metronidazole susceptible strains and 22% (2/9, 95% CI: 3–60%) for resistant strains (P = 0.0001). Conclusion : Both regimens are effective in metronidazole susceptible strains. However, in contrast to the amoxycillin-containing regimen, that containing clarithromycin is also effective in resistant strains.