The dynamic of granulocytic macrophages and erythroid precursors content in bone marrow of CBA mice, irradiated by 2.0 Gy and the level of colony-stimulating and erythropoietic activities in supernatant of bone marrow myelocariocytes and blood serum were studied. The process of haemopoiesis regeneration was accompanied by increasing of the values of these indexes in bone marrow and peripheral blood. The treatment of bone marrow cells by monoclonal antibodies to Thy 1.2 antigens resulted in decreasing of myeloid precursors and diminishing of colony-stimulating activity of bone marrow cells supernatant.