OBJECTIVE The aim of this study was to compare the efficacy and side effects of 1-wk triple therapy with ranitidine bismuth citrate (RBC) 400 mg b.i.d., clarithromycin 500 mg b.i.d., and metronidazole 500 mg b.i.d., to 2-wk dual therapy with RBC 400 mg b.i.d. and clarithromycin 500 mg b.i.d. for H. pylori infection in a randomized, clinical trial. METHODS Patients (18-80 yr) with a culture proven H. pylori infection were randomized to one of these regimens. Side effects were scored on a semiquantitative scale. Endoscopy was performed > or = 4 wk after treatment. Antral biopsy samples were taken for hematoxylin-eosin stain (HE), rapid urease test, and culture and corpus samples for culture and HE. Two weeks after the endoscopy, a 13C-urea breath test was performed. Eradication failure was defined as detection of H. pylori by culture or by at least two other tests. RESULTS A total of 104 patients, 54 men, age 54+/-14 yr, (36 duodenal ulcer, 16 gastric ulcer, and 52 functional dyspepsia) were included. Gender, age, and diagnosis were comparable in both groups. Fourteen of 52 patients in both triple and dual therapy, respectively, had significant side effects, but all patients completed the course. Eradication results were 49 of 52 (94%; 95% CI: 84-99%) and 50 of 52 (96%; 95% CI: 87-100%) on intention to treat analysis and 44 of 46 (96%; 95% CI: 85-99%) and 48 of 49 (98%; 95% CI: 89-100%) on per protocol analysis for triple and dual therapy respectively. CONCLUSIONS Both regimens are very effective and well tolerated in the treatment of H. pylori infection. The triple regimen has the advantage of being shorter.