The favorable clinical results obtained with tumor necrosis factor(TNF) and interleukin-1 (IL-1) inhibitors may suggest that the story of the contribution of cytokines to arthritis is almost over. However, additional cytokines that may contribute to joint inflammation have been described. Among these, IL-17 is of interest in this context, for two major reasons: first, similar to TNF and IL-1, IL-17 has proinflammatory properties, and second, it is produced by T cells. Since the role of T cells has been a matter of debate, demonstration of the contribution of IL-17 to arthritis would also imply a role for the IL-17–producing T cells themselves. These issues are important, since they may lead to new therapeutic applications.