The following specificcharacteristics of the composition of intestinal microbiota in patients with irritable bowel syndrome (IBS) were identified using a metagenomic analysis (16 S rRNA): 1) an increase in the representation of Actinobacteria, including Bifidobacterium spp., Firmicutes, including representatives of Streptococcaceae (Streptococcus), Lachnosperaceae (Dorea), Veillonellaceae (Dialister), Proteobacteria (Enterobacteriaceae and Desulfovibrionaceae families); 2) a decrease in the population of Bacteroidetes, including representatives of the families Prevotellacea (Prevotella spp.), Bacteroidaceae (Bacteroides spp.). Firmicutes belonging to the families Clostridiaceae and Ruminococcaceae (Fecalibacterium spp.).Flow cytometry in the study of the subpopulation composition of T regulatory (Treg) lymphocytes in patients with IBS revealed an increase in the number of CD45R0+CD62L+ central memory cells (CM), which can regulate the processes of maturation and differentiation of lymphocytes in lymphoid tiss