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Summary. The study of the indirect effect of cytokines is relevant. IL-2, in turn, has a significant effect on the hematopoietic system, both in clinical and experimental studies. The target cells of IL-2 are T- and B-lymphocytes, monocytes/macrophages, NK cells, dendritic cells and other cells on which specific membrane receptors are expressed. Because IL-2 is at the top of the cytokine cascade, any alteration in IL-2 signaling, especially under stress, will rapidly upregulate the homeostatic balance in the bone marrow, leading to major shifts in proliferation. Thus, IL-2 has an effect both on the hematopoietic process and on peripheral blood cells. The aim of the study – to investigate the effect of IL-2 on the bone marrow cells of mice under conditions of physical training. Materials and Methods. The study was conducted on sexually mature male laboratory mice for 6 weeks. Five experimental and one control (without physical training) groups of animals were formed. Group 1 received IL-2 inhibitor (Cyclosporin) (10 mg/kg), Groups 2, 3 and 4 received IL-2 (Roncoleukin) in concentrations of 5000, 7500 and 30000 IU/kg, respectively, Group 5 received sterile physiological solution. The method of forced swimming to exhaustion with a load was used as physical training. Femur bones were isolated from experimental animals and bone marrow impressions were obtained, which were stained with May-Grunwald-Giemsa dye and the population of bone marrow cells and their percentage ratio (myelogram) were counted using an immersion microscope system. The neutrophil maturation index and the leuko-erythroblastic ratio were also mathematically calculated at each stage of the study. Results. Compared to the control in the 6th Week of the study, the number of basophilic normoblasts was lower in all experimental groups except the 2nd, the decrease ranged from 37.5 % – Group 1 to 87.5 % – Group 4. The number of segmented neutrophils was significantly higher in all experimental groups, regardless of exposure. This may be the result of physical training, but under the influence of IL-2 in the average concentration, the indicator was the highest. Also, the number of promyelocytes was significantly lower than the control in Groups 1, 2 and 3 (by 55.8; 67.4 and 44.2 %), and metamyelocytes – in Groups 2, 3 and 4 (by 48.4; 38, 7 and 54.8 %). At the same time, the number of lymphocytes was higher in Groups 1 and 2 by 105.6 % and 138.8 %, respectively. The content of basophils was higher than the control in Groups 2 and 3 by 4 times, in Group 4 by 7.3 times. Against this background, the content of eosinophils, pronormoblasts, oxyphilic normoblasts and plasma cells did not undergo significant changes. Conclusions. IL-2 clearly affects myelopoiesis in the hematopoietic system. Heterogeneous changes in bone marrow indicators were noted in experimental groups of animals. It was shown that IL-2 in all concentrations had an effect on increasing the leuko-erythroblastic ratio, the most in high concentration, which indicates hyperplasia of leukopoiesis cells as in intoxication. An increase in the absolute content of mature forms of neutrophils was established in animals with the introduction of IL-2 in low and medium concentrations, which led to a decrease in the neutrophil maturation index (by 55.1 % and 39.7 %)