The colony-stimulating factors (CSFs) are the master regulators of granulocyte and macrophage populations. There are four different aspects of the connection between the CSFs and cancer: (a) the CSFs can accelerate the regeneration of protective white cells damaged by chemotherapy; (b) the CSFs can mobilize stem cells to the peripheral blood in convenient numbers for transplantation; (c) the CSFs can enhance anticancer immune responses and (d) the CSFs are potentially involved in the genesis of the myeloid leukemias.