In hepatology nucleic acids (usually preparation nucleinate) are usually administered to patients with chronic hepatitis C, who receive interferon therapy, for stimulation of leucopoiesis. However, nucleic acids have a significantly wider spectrum of biological action. Results of experimental investigations concerning influence of milk bacterialyeast beverage with a considerable content of nucleic acids on different functions of the body have been presented in our research. Materials and methods. Milk bacterial1yeast beverage, containing nucleic acids, was tested. Authors also elaborated technique of koumiss production in dry state (content of DNA – 0,76 mg/g, and RNA – 0,61 mg/g). Mechanism of immunopotentiating action of koumiss from cow’s milk was studied in experiment on animals and birds. Immunopotantiating action of the beverage on human beings was estimated by its influence on the efficacy of preventive immunization against diphtheria. Results. In experiment on piglets it was established that administration of food supplement promoted probable decrease in incidence of gastrointestinal diseases: in experimental group 10% of piglets were ill during observation period, in control group – 70,9%. Average haematological indices, content of erythrocytes and haemoglobin in experimental group of piglets, were higher and constituted 8,14± 0,32 million and 8,16±0,37 g% respectively, and in control group – 7,95±3,4 million and 7,57±0,38 g% respectively (Р 1:1280, constituted only 60%, in experimental – 100%. The obtained data concerning influence of koumiss on synthesis of antitoxin confirm its immunopotentiating action and simultaneously indicate expediency of administration of immunostimulants during vaccination. Conclusions. It has been established that food supplement has a considerable biological activity, in particular, it influences positively immunity indices. In our opinion, it is important that besides high content of ribonucleic acid (1800–2100 mcg/ml), the beverage contains complete set of essential amino acids, glutamine acid (to 6 g/l), vitamins from B group and other useful substances (all components in optimal ratio). Adding of milk bacterial-yeast beverage with high content of nucleic acids to patients’ diet has certain advantages over pharmacological preparations.