Purpose: to study bone marrow mast cells in mice after autotransplantation. Materials and methods. Mast cells and sulphatedness degree of heparin mucopolysaccharide in the bone marrow were identified using Unna staining with polychromatic toluidine blue. Study results. Data on mast cells distribution in the bone marrow after autotransplantation in 40 minutes and in 2 hours were analyzed. Two types of mast cells’ reaction to autologous bone marrow introduction were identified: sequential degranulation and exocytosis. As a result, secretion of mast cells causes production of biologically active substances in the microenvironment of a mast cell; these substances form chains and conglomerates from granules, changes in the number of which can contribute to changing the process of mitotic division. According to morphological criteria three populations of mast cells were identified: small-sized cells, with blue-colored nuclei stained orthochromatically and located asymmetrically; metachromatic oval-shaped cells with a nucleus located in the centre; large, degranulated, gamma-metachromatic mast cells. Most part of mast cells in bone marrow smears is presented by integral forms. Heparin in mast cells takes part in regulating metabolism in the bone marrow after autotransplantation.