We demonstrated the phenotypic characteristics of T cells interacted with synovial fibroblast-like cells. A small percentage of peripheral blood T cells adhered to synovial fibroblast-like cells. When synovial cells were treated with interferon-gamma or interleukin-1 beta, the percentage of T cells that adhered to the treated cells markedly increased in comparison with the value for untreated synovial cells. The kinesis of T cell adherence to treated synovial cells differed from that of HLA-DR antigen expression on synovial cells. T cell adherence was not blocked by mouse monoclonal anti-HLA-DR and anti-HLA-ABC antibodies. The phenotypes of the adherent and nonadherent T cells were investigated with a flow cytometer. The CD29 + subset was more adhesive than the CD45RA + subset to IL-1 beta-stimulated synovial cells. The proportions of high density lymphocyte function associated antigen (LFA)-1 alpha and LFA-1 beta were greater in the adherent than in the nonadherent T cells, and the mean fluorescence intensities of LFA-1 alpha, LFA-1 beta and CD2 molecules on adherent T cells were significantly higher than those on nonadherent T cells. Our results support the concept that an interaction between infiltrating lymphocytes and synovial cells occurs in the synovium, resulting in the initiation and perpetuation of immune responses in synovial tissue in rheumatoid arthritis.