The objective of the research study was to assess the survivability of probiotic strains of Lactobacillus spp. and Saccharomyces cerevisiae under the model conditions that simulated selected sections of the digestive tract of poultry. The strains tested were administered to the animals without feed or with feed. The microorganisms as named above are included in the newly developed probiotic mixtures (A, B and C). The survivability of the bacteria and yeasts tested under the simulated conditions of the crop, gizzard and small intestine was determined using a culture method. Initially the average count of Lactobacillus spp. was 1.00 – 1.95 × 10⁹ CFU/ml, while the average count of yeast was 1.04 – 3.00 × 10⁷ CFU/ml. As a result of the passage of samples without feed, the count of bacteria and yeast was reduced in the subsequent sections of the simulated digestive tract; in the small intestine it was, on average, 2 orders of magnitude lower. However in the case of the feed with probiotic mixtures, the count  of Lactobacillus spp. in the small intestine was, on average, 1 order of magnitude higher and that of yeast, on  average, 1.5 orders of magnitude higher compared to the mixtures without feed. Thus, the added feed constituted a  protective factor against the adverse conditions of the environment of digestive tract under the model study.  Based on the results obtained, it is concluded that probiotic mixtures may be potentially applied as an additive in feeds intended for poultry.