The most widely used model for rheumatoid arthritis is the collagen-induced arthritis (CIA) in mice. This model has gained acceptance since it is reproducible, well defined and has proven useful for development of new therapies for rheumatoid arthritis, as exemplified by the most recent advancement using TNFalpha neutralization treatment. The collagen-induced arthritis model, however, represents only certain pathways leading to arthritis and there is no consensus on how they operate. Nevertheless, we are beginning to understand the immune recognition structures, such as MHC molecules, lymphocyte receptors and type II collagen epitopes, which are of crucial importance for the development of this disease. These provide useful tools for further investigations of the pathogenesis of CIA as well as for understanding the pathogenesis of rheumatoid arthritis.