Aim. Detection of properties of the dominant microsymbiont emerging in the course of interaction of associative symbiosis components and ensuring protection of vaginal mucosa from seeding by pathogens. Materials and methods. H 2O 2-producing Lactobacillus spp., Corynebacterium spp., Staphylococcus aureus, Escherichia coli and primary epitheliocytes from lower reproductive tract of women were used. The ability of Lactobacillus spp. to influence changes of synthesis of catalase inhibitors by corynebacteria, bactericidal activity of lysozyme, lactoferrin and thrombocyte antimicrobial protein, antimicrobial activity of primary vaginal epitheliocytes was evaluated. Changes of antagonistic and growth properties of lactobacilli during interaction with secretory products of Corynebacterium spp., S. aureus, E. coli and vaginal epitheliocytes were also studied. Results. Exometabolites of both epithe-liocytes and corynebacteria were revealed to stimulate in most cases lactobacilli biomass growth and increased their antagonistic activity against S. aureus и E. coli. Metabolites of H 2O 2-producing lacto- bacilli increased synthesis of antimicrobial substances by epitheliocytes and potentiated bactericidity of natural resistance factors. Under the influence of lactobacilli metabolites an increase of production of catalase inhibitors by corynebacteria was revealed. Conclusion. Symbiotic interrelations of dominant microorganisms with host organism and associants under the condition of associative symbiosis leading to stimulation of production and potentiating of the effect of antibacterial protection factors are the basis for colonization resistance of vaginal biotope.