In previous researches, three strains of Lactic Acid Bacteria with probiotic properties have been defined: Lactobacillus acidophilus M92, Lactobacillus plantarum L4 and Enterococcus faecium L3. Probiotic strain of L. acidophilus M92 has shown the highest immunomodulatory properties that could be attributed to the paracrystalline layer so called S-layer protein. Besides stimulating the synthesis of total IgA, IgG and IgM antibodies in immunized mice serum, S protein influences enhanced survival of L. acidophilus M92 under simulated conditions of gastric juice and intestinal juice, proving its protective function. Also, adhesive function of L. acidophilus M92 S protein has been shown on epithelial cells of mice small and large intestine in vitro as well as in vivo tests. The assimilation of probiotic substrates with selected lactic acid bacteria has been realized in vivo, with experimental Swiss Albino mice. The best synbiotic preparations, so far, have been: Lactobacillus acidophilus M92 in combination with inulin, Lactobacillus plantarum L4, and Enterococcus faecium L3 in combination with lactulose. The immunomodulatory effect on tested probiotic strains and prebiotic substrates on immunity system of mice was explored by ELISA method. Immunizing mice orally with synbiotic preparations has caused stronger immune response than individual probiotic strains and prebiotic substrates. Only synbiotic L. acidophilus M92, L. plantarum L4 and E. faecium L3 preparations using various prebiotic substrates have shown positive influence on intestinal microflora in mice due to the competitive exclusion of undesirable members of intestinal microflora, enterobacteria and sulphite reducing clostridia. The a adhesive function of tested probiotic strains in the small and large intestine of experimental mice has been confirmed by inducing the resistance of these strains on rimfampicin, and by identification of bacterial strains isolated from mice intestine by using RAPD-PCR method.