Interleukin 17 (IL-17) is a family of pro-inflammatory cytokines produced by activated T cells and is thought to have a major role in the initiation and perpetuation of rheumatoid arthritis. IL-17 regulates the activities of NF-κB and mitogen-activated protein kinases such as ERK and JNK. In addition, IL-17 stimulates the expression of IL-6 and cyclooxygenase-2 and enhances the production of nitric oxide. IL-17-producing T helper cells (TH-17 cells) have been the subject of much attention due to the importance of IL-17 in the pathogenesis of autoimmune inflammation. Because of its role in autoimmune diseases, it is thought that targeting the production and action of IL-17 would be beneficial therapeutically in these diseases.