Two new models for the study of rheumatoid arthritis have been established. SCID (severe combined immunodeficient) mice implanted with human synovial tissues and human HLA-DR4-CD4 transgenic mice represent novel and important approaches to the use of animal models in pathogenetic studies. New studies of streptococcal cell wall arthritis in rats demonstrated that beta 1 integrin-mediated cell-matrix interactions are involved in the induction and perpetuation of inflammatory synovitis and that systemic administration of interleukin-4 selectively suppresses established synovitis, presumably by effects on monocyte function. The importance of nitric oxide as a mediator of synovial inflammation was confirmed in the adjuvant-induced model of rheumatoid arthritis. In the collagen-induced arthritis model, interesting new data have implicated gamma delta T cells in the pathogenesis of arthritis, and the antineoplastic drug taxol was shown to have anti-inflammatory effects.