One of major functions of lactic acid bacteria is their participation in the formation of local and systemic immune resistance of the host. The lactic acid bacteria associated with the mucous coat of the gastro-intestinal tract are cooperating with epitheliocytes, M-cells of Peyer's patches and various cells of the immune system. As a result of processing and presentation of specific cell components, lactic acid bacteria use mechanisms of modulation of cell-dependent immune response, activate RES and stimulate cytokine production. The article gives data on the role of lactic acid bacteria in the formation of T-and B-cell immune response, production of pro-inflammatory and anti-inflammatory cytokines ensuring the balance between humoral and cell-dependent immunity. The mechanisms of antitumor and oncostatic activity of lactic acid bacteria are analyzed. The polyfunctional influence of lactic acid bacteria on the immune reactions of the macroorganism includes the enhancement of the activity of monocyto-macrophages, natural killers and cytotoxic lymphocytes, modulation of reactions of the T- and B-cell immune responses, i.e. the complex system of interaction being formed between the indigenous intestinal microflora and the macroorganism is the basis of the normal function of its immune system.