The aim of this study is to investigate the effects of Bifidobacterium lactis B94 and inulin (synbiotic) treatment on eradication rate and patient compliance in subjects treated for symptomatic H. pylori infection. Patients with symptomatic H. pylori infection were divided into two groups. One group was treated with standard triple therapy (lansoprazole, amoxicillin, and clarithromycin) and B. lactis B94 (5 x 10(9) CFU/dose) plus inulin (900 mg) twice daily for seven days. The control group was treated with standard triple therapy and placebo. The side effects and eradication rates were evaluated at the end of the study. Ninety-three patients with H. pylori infection were treated with either synbiotic plus triple therapy (n = 47) or placebo plus triple therapy (n = 46). The infection eradication rates were not significantly different between the synbiotic and placebo groups [intent-to-treat (ITT), 80.8% and 67.3%, p = 0.13, respectively; per-protocol (PP), 86.3% and 81.5%, p = 0.55, respectively]. The drug side effects were significantly higher in the placebo group than in the synbiotic group (63% and 17%, respectively, p < 0.01). Although no intolerable adverse side effects were observed in the synbiotic group, intolerable adverse side effects were observed in 13% of the placebo group (p = 0.01). Our results suggest that twice daily 5 x 10(9) CFU/dose B. lactis B94 plus 900 mg inulin treatment did not have a direct positive effect on the H. pylori eradication rate. However, this treatment had significantly reduced side effects and indirectly increased eradication rates by increasing patient compliance.