<p>We studied the effect of metabolites produced by lactobacilli on the metabolic and killing activities of neutrophil. Treatment with lactic acid at a concentration of 5.6 mM increased dehydrogenase activity and killing activity of neutrophils and slightly decreased the mitochondrial potential in cells; at concentrations of 11.1 and 22.2 mM, lactate decreased dehydrogenase activity, which was accompanied by a decrease in the mitochondrial potential in cells; at a concentration of 11.1 mM, lactate decreased killing activity of neutrophils. Hydrogen peroxide increased the dehydrogenase and killing activities at concentrations of 0.59 and 2.36 mM and decreased these parameters at a concentration of 1.18 mM; these changes were accompanied by a decrease in the number of cells with high mitochondrial potential. It is assumed that the ability of vaginal lactobacilli to modulate neutrophil activity has important evolutionary significance and allows regulating the number of opportunistic microorganisms.</p>