BACKGROUND In vitro experiments with Lactobacillus acidophilus have revealed its inhibitory effect on Helicobacter pylori and its application in treatment of Helicobacter pylori positive gastritis was examined. METHODS 15 patients have undergone gastroscopy with biopsy and by histopathological examination. Helicobacter pylori positive gastritis was detected. During a two-month period these patients took acidophilus milk (3 x 250 ml a day) prepared according to a special protocol and which contained 4 x 10(9)-1 x 10(10) live cells of Lactobacillus acidophilus at the moment of preparation. Lactobacillus acidophilus strain NAS, gained from lyophilized preparation Bio-Nate (Natren Inc. USA) was used as a test organism. Control gastroscopy was performed 2 months later. RESULTS 14 patients have completed the examination. All of them were satisfied with the taste of acidophilus milk and could stand it well, whereas in 6 out of 14 Helicobacter pylori was eradicated. CONCLUSIONS Helicobacter pylori eradication therapy is recommended in all cases of Helicobacter pylori positive gastritis associated with peptic ulcer, as well as in absence of ulcer when subjective difficulties occur. Antibiotic therapy is often unsuccessful and most often associated with risks of significant adverse effects, being the consequence of intestinal microflora disorders. The aim of using Lactobacillus acidophilus in the therapy is to reduce risks of adverse effects. In our study, by using acidophilus milk only, without other therapy, eradication of Helicobacter pylori was achieved in 6 out of 14 patients. All patients could stand the therapy well and were satisfied with the taste of the preparation. The number of examinees was small in regard to making conclusions, but the results are encouraging and show that apart from established in vitro effect. Lactobacillus acidophilus has a potential in vivo effect.