In this review the involvement of T cells, in addition to that of the monocyte/macrophage lineage, in the pathogenesis of rheumatoid arthritis is discussed. The evidence for the pathogenetic importance of T cells is based upon their state of activation in the synovial membrane and the cytokines produced. These cytokines can be detected in synovial fluids as well as in the synovial membrane by both immunohistochemistry and in situ hybridization. However, cytokine production can be detected only in a minor fraction of the T cells which contrasts the number of non-T cells observed to synthesize cytokines. Nevertheless, it can be assumed that the small amount of lymphokines is sufficient to activate a cytokine cascade derived from other cells. The cytokine profile secreted is indicative for a T cell response that primarily involves Th1-like cells.