The objective of this study was to assess the efficacy of a new regimen in eradicating Helicobacter pylori (Hp) in patients with duodenal ulcer (DU) who were previously treated unsuccessfully with standard triple therapy (tripotassium dicitratobismuthate [TDB] 120 mg QID, metronidazole 500 mg TID, and tetracycline 500 mg QID) or proton-pump inhibitor (PPI) dual therapy (omeprazole 20 mg BID and amoxicillin 500 mg QID). The study included 133 consecutive patients aged 17 to 83 years with endoscopically diagnosed DU (diameter > or = 5 mm) in whom standard triple therapy or PPI dual therapy had failed to eradicate Hp. A rapid urease (CLO) test was performed on four biopsy specimens at study entry and at least 1 month after the end of treatment to confirm Hp colonization and eradication, respectively. Patients were considered to be Hp positive if any CLO test was positive within 2 hours, and Hp was considered to be eradicated if all CLO tests were still negative after 24 hours. In 31 randomly selected patients, Hp eradication was confirmed histologically as well. Patients were given omeprazole 60 mg/d (20 mg in the morning and 40 mg in the evening) plus amoxicillin 500 mg QID for 10 days and subsequently were given metronidazole 500 mg TID for 10 days plus TDB 120 mg QID for 6 weeks. One hundred and twenty-four patients were followed up; five (4%) withdrew because of side effects (protracted diarrhea, stomatitis, skin rashes). Per-protocol analysis showed Hp eradication in 113 of 119 patients (95%) and ulcer healing in 118 of 119 (99%). Intent-to-treat analysis showed an Hp eradication rate of 85% (113 of 133 patients) and an ulcer healing rate of 89% (118 of 133 patients). In per-therapy analysis, the Hp eradication rate was 91% (113 of 124 patients), and the ulcer healing rate was 95% (118 of 124 patients). Side effects were observed in 39 of 119 patients (33%) and were generally mild. The four-drug regimen used in this study, when given to patients previously treated unsuccessfully with standard triple therapy or PPI dual therapy, was highly effective in eradicating Hp and healing DUs and had no major side effects.