Human M-CSF, also known as CSF-1, can be either expressed on the cell surface as a membrane-spanning 68-86 kDa chondroitin or secreted as an 80-100 kDa glycoprotein or 130-160 kDa chondroitin sulfate-containing proteoglycan. The biologically active forms of M-CSF are dimeric. The following tissues are known producers of M-CSF: submaxillary gland, lung, spleen, kidney, lymph nodes, brain, liver, testis, ovary, and some human tumors. M-CSF can be synthesized in most cell types including fibroblasts, endothelial cells, bone marrow stromal cells, osteoblasts, thymic epithelial cells, keratinocytes, astrocytes, myoblasts, mesothelial cells, liver parenchymal cells, thyrocytes, and adipocytes. The primary biological activities of M-CSF are related to the survival, proliferation, and differentiation of mononuclear phagocytes. Many conditions are accompanied by elevated M-CSF levels, such as pregnancy, neoplastic disorders of hematopoietic and reproductive systems, pre-edampsia, chemotherapy with and without autologous bone marrow transplantation, infection, liver disease, hepatic injury, hemophagocytic syndrome, thalassemia, amyloidosis, ischemic heart disease, ovarian cancer, endometrial cancer, breast cancer, and amyloidosis. The human M-CSF gene has a length of approximately 20 kb and contains ten exons. The gene has recently been assigned to chromosome 1p13-p212, which is in the vicinity of the amylase genes. IL-2 induces gene expression of M-CSF in human blood-derived monocytes, and NF-kappa B is involved in transcriptional regulation of the M-CSF gene. A genetic variation of the M-CSF gene exists in humans and appears to substantially increase atherosclerosis risk among smokers. The biological activities of M-CSF are mediated by a receptor of 165 kDa in length encoded by a gene that maps to human chromosome 5q33. The M-CSF receptor is identical with the proto-oncogene fms, and has been subsequently named CD115. This M-CSF ELISA is a ready-to-use 4 hours solid phase immunoassay readily capable of measuring M-CSF levels in serum, plasma and cell culture supernatant in the range of 0 to 4000 pg/mL. This assay has shown no cross-reactivity with other cytokines tested, and is expected to be used effectively for further investigations into the relationship between M-CSF and the various conditions mentioned.