The recruitment of leukocytes into the joint is a fundamental process observed in arthritis. Evidence suggests that the pro-inflammatory cytokines, such as tumor necrosis factor α (TNFα), interleukin (IL)-1 and IL-8, are involved in the recruitment of leukocytes. These proinflammatory cytokines have been postulated to be linked in a network. This notion is, however, mainly based on the findings obtained in vitro. Extrapolation of in vitro results to in vivo situations must be taken with caution. Animal models of arthritis are useful for understanding the role of cytokines and the related network that is operative in the joint.