Macrophage colony stimulating factor (M-CSF) is one of the glycoproteins called colony-stimulating factors (CSFs). Granulocyte/macrophage colony-stimulating factors are cytokines that act in hematopoiesis by controlling the production, differentiation, and function of 2 related white cell populations of the blood: the granulocytes and the monocytes-macrophages. M-CSF is synthesized by mesenchymal cells. This cytokine stimulates the survival, proliferation, and differentiation of hematopoietic cells of the monocyte-macrophage series. Some clinical investigations have shown autologous production of M-CSF various human cell lines in vitro and by tumors in vivo. Human MCSF shows activity on mouse cells whereas mouse MCSF shows no activity on human cells. Recombinant Human M-CSF produced in E. coli is a disulfide linked homodimer, non-glycosylated, polypeptide chain containing 2 x 159 amino acids with a MW of 36.8 kDa.