BACKGROUND/AIMS: The optimal regimen for the eradication of H. pylori remains unclear. Thus the authors evaluated the effect of one-week course of omeprazole quadruple regimen on eradication o H. pylori in Korea. METHODS: We investigated the outcome of quadruple therapy on eradication o H. pylori in 93 patients with H. pylori positive gastritis or peptic ulcer diseases. We tried three different quadruple regimens. were A quadruple regimen (OBMA) including omeprazole 20 mg b.i.d.amoxicillin 1 g b.i.d., metronidazole 500 mg t.i.d. and bismuth 240 mg b.i.d. was used for 64 pati ents. Another regimen (OABC) including omeprazole 20 mg b.i.d., amoxicillin 500 mg t.i.d., bismuth 240 mg b.i.d. and clarithromycin 250 mg b.i.d. was used for 18 patients and the third regimen (OAMC) including omeprazole 20 mg b.i.d., amoxicillin 1 g b.i.d., metronidazole 500 mg t.i.d. and clarithromycin 250 mg b.i.d. (OAMC) was applied for 11 patients. RESULTS: The overall eradication rate of quadruple regimens was 84.9%. Eradication rates of each regimen were 94.4% in OABC 81.9% in OAMC and 82.8% in OBMA. Eradication was successful in 85.2% of 61 patients who used quadruple regimen as first line treatment and in 84.4% of 32 patients who used quadruple regimen for retreatment. The side effects were observed in 16.1% of the patients and the compliance rate wa 98.9%. CONCLUSIONS: One-week course of quadruple regimens was effective in the eradication of H pylori and showed good compliance. Quadruple regimen was also effective in patients who failed to eradicate H. pylori with dual or triple regimen.