Modern molecular genetic methods of research, which emerged in the 21st century, completely unfixed all established notions not only about the microcosm, but also about its influence on the life and health of the macroorganism. The identification of intestinal bacteria and particularities of their various strains is increasingly expanding our understanding of the mechanisms of their action on the somatic and mental health of a human being. The various lactobacilli strains have been the most studied probiotic at the present time. The genus Lactobacillus is known to include about 90 species with a wide range of biochemical and physiological properties. Lactobacillus reuteri, which has strains with different mechanisms of action, is one of the unique microorganisms of the family Lactobacillaceae. The range of possibilities for using various Lactobacillus reuteri strains is currently very wide. This article deals with clinical effects associated with the strain-specificity of Lactobacillus reuteri.