Granulocyte-colony stimulating factor (G-CSF) is a growth factor and an essential cytokine belonging to the CSF family of hormone-like glycoproteins that regulate haematopoietic cell proliferation and differentiation. G-CSF was isolated initially as a factor supporting the growth of colonies of granulocytes in soft agar cultures. Cells of the monocyte/macrophage lineage are among the most prominent sources of G-CSF, but this factor can also be produced by normal cells of mesodermal origin, including vascular endothelial cells, fibroblasts, and mesothelial cells. Production of G-CSF can be induced in vitro in these cells by a wide variety of stimulatory agents, including LPS, TNF, IL-1, IL-3, I L-4, and IFN-Gamma. G-CSF is likely to play a role in the basal regulation of neutrophil production, and also functions as a primary regulatory factor controlling the neutrophil response to inflammatory stimuli. Furthermore, G-CSF exhibits other biological activities besides the proliferative effects, since G-CSF appears to modulate the distribution of neutrophils and progenitor cells within the body.