The mechanisms of granulocytopoiesis stimulation with granulocytic CSF (neupogen), added to chemotherapy protocol (adriablastine+taxotere) in patients with stages III-IV breast cancer, were studied. The hemostimulatory effect of granulocytic CSF preparation is based on stimulation of proliferation and differentiation of granulomonocytopoisis precursor cell in the hemopoietic tissue, due to neupogen effects on hemopoietic elements and on the hemopoiesis-inducing microenvironment cells.