Interleukin -17A (IL-17A) is a secreted, homodimeric glycoprotein linked by disulfide link with a molecular mass of 35 KiloDalton. The cytokine is the proto-type of a newly discovered pro-inflammatory cytokine family which consists of IL-17A, IL-17B, IL-17C, IL-17D, IL-17E (IL-25) and IL-17F. All the IL-17s have similar structure with four highly conserved cysteine residues and same 3 dimensional structures, which distinguish this family from other cytokines. IL-17 is produced by a group of CD4 T help cells termed Th17 cells. In addition to previous discovered Th1 and Th2 cells, the Th17 cells consist in the third group of T help cells. IL-23, a growth and stabilization factor was the first cytokine that was found to involve with the development of Th 17 cells. Later on, other cytokines including TGF-beta, IL-6, IL-21 were also found to contribute to the procedure. The transcription factors implicated in the procedure were identified asSTAT3, RORgt, and RORa. IL-17, like interferon-g, is a potent mediator of delayed-type reaction. IL-17 induces the secretion of many other pro-inflammatory cytokines and chemokines such as IL-6, IL-8, GM-CSF, G-CSF, TGF-beta, TNF-alpha,GRO-alpha, MCP-1, and stimulates the expression of NF-kappaB, mitogen activated protein kinase, and prostaglandings from many cell types. By stimulating cytokine production and recruiting monocytes neutrophils to site of inflammation, the cytokine exerts its effect in response to tissue damage and invasion. Excessive expression of IL-17 was found to associate with autoimmune diseases and chronic inflammatory diseases such as multiple sclerosis, rheumatoid arthritis, psoriasis, inflammatory bowel diseases, tissue allograft rejection, allergic asthma and infectious diseases at the mucosal tissue. This IL-17A ELISA is a 3.5-hour solid phase immunoassay readily applicable to measure IL-17A levels in serum, plasma, cell culture supernatant, and other biological fluids in the range of 0 to 1000 pg/mL. It showed no cross reactivity with other cytokines tested. This IL-17A ELISA is expected to be effectively used for further investigations into the relationship between IL-17A and the various conditions mentioned.