Tumor necrosis factor-alpha (TNF alpha) is one of several pro-inflammatory cytokines that have been implicated in the pathogenesis of Crohn's disease (CD). Treatment with antibodies to TNF alpha has been shown to reduce mucosal inflammation in the disease, promote tissue healing, achieve and maintain remission, improve the CD activity index (CDAI) and improve the quality of life. The first part of this article reviews the role of TNF alpha in CD.