FOUR colony-stimulating factors influence the survival, proliferation, differentiation, and functional activation of myeloid hematopoietic cells: macrophage colony-stimulating factor (M-CSF), granulocyte colony-stimulating factor (G-CSF), granulocytemacrophage colony-stimulating factor (GM-CSF), and interleukin-3 (formerly known as multi-colony-stimulating factor).1 2 3 Various other cytokines and factors are also implicated in these processes, including interleukins 1, 5, 6, and 11 and the recently identified Steel factor (variously designated c-kit ligand, mast-cell growth factor, and stem-cell factor).4 , 5 Of these factors, only G-CSF and GM-CSF are commercially available for clinical use. G-CSF has been approved in the United States and major European countries for the reduction of infection after . . .