G-CSF is secreted by monocytes, macrophages, and neutrophils after cell activation. It is also produced by stromal cells, fibroblasts, endothelial cells, epithelial carcinomas, acute myeloid leukemia cells, and various tumor cell lines. The synthesis of G-CSF can be induced by bacterial endotoxins, TNF, IL1 and GM-CSF. Comparison of the primary sequence of G-CSF with those of GM-CSF and M-CSF, shows that the three factors are not related to each other. Murine and human G-CSF share a sequence homology (protein) of approximately 70% and exhibit cross reactivity. G-CSF stimulates the proliferation and differentiation of hematopoietic progenitor cells committed to the neutrophils and granulocytes lineage in a dose-dependent manner. Expressed in human 293 cells, it is a monomeric glycoprotein with a molecular mass of 21 to 25 kDa.