Literature reporting activity of probiotics in infections due to Helicobacter pylori has been reviewed to assess their value in combating such infections. Several in vitro studies show that lactobacilli or their cell-free cultures inhibit or kill H. pylori, prevent its adhesion to mammalian epithelial cells and prevent IL8 release. In vivo models demonstrate that pre-treatment with a probiotic can prevent H. pylori infections and/or that administration of probiotics markedly reduced an existing infection. Thirteen clinical trials have been published. In six (180 patients), a probiotic was used alone; five of these had an encouraging result-in three there were significantly reduced breath test readings and in two others some patients were cleared of infection. In seven further trials (682 patients), probiotics were added to a therapeutic regimen of antibiotics, resulting in an increased cure rate in two studies, and reduced side-effects in four. Trials in which fermented milk products or whole cultures of lactobacilli were used tended to show better results than when the probiotic was taken in the form of bacteria alone. Not all the studies were randomised, double-blind and placebo controlled, and some involved only small numbers of patients. The results suggest that probiotics may have a place as adjunctive treatment in H. pylori infections and possibly in prophylaxis. Future trials should address in particular the type of patient (asymptomatic volunteers, symptomatic patients), choice of probiotic strain(s), a wide range of probiotic strains (Lactobacillus acidophilus, L. johnsonii, L. gasseri, lactobacillus GG, Bifidobacterium longum, and bioyoghurts) have been used-some non-viable, regimens (doses and duration) and criteria of success (breath test, histology, culture, serology).