In the present study we revealed a common reaction of cells of the mononuclear phagocyte system in the central and peripheral immunopoietic organs and pancreas in rats with chronic hyperglycemia. The activation of monocytopoiesis and recruitment of mononuclear phagocytes in peripheral tissues were observed. The modulation of functional activity of mononuclear phagocytes by 3-aminophthal- hydrazide contributes to normalization of monocytopoietic intensity and a decrease in the level of macrophagal infiltration in thymus, pancreas and peripancreatic lymph nodes. These changes indicate that mononuclear phagocytes are involved in adaptive response of the organism to chronic hyperglycemia.