Monoclonal antibodies with specificities for various human T-cell antigens were used in direct immunofluorescence to quantify the proportions of T lymphocytes with suppressor/cytotoxic-cell markers and with helper/inducer-cell markers and of T lymphocytes with HLA-DR antigens. Normal percentages of lymphocytes with suppressor/cytotoxic-cell markers were detected in the peripheral blood synovial fluid and synovial tissue lymphocytes from patients with juvenile rheumatoid arthritis (JRA) and rheumatoid arthritis (RA), respectively. Normal percentages of T lymphocytes with helper/inducer-cell markers were seen in the peripheral blood of RA and JRA patients and in the synovial tissues of RA patients. Slightly decreased percentages of cells with the helper/inducer-cell marker were detected in the synovial fluids of JRA patients. The proportions of HLA-DR-positive T lymphocytes were highly increased in the synovial fluid and synovial tissue, whereas the numbers of these cells in the peripheral blood were normal. No significant differences in T gamma cells were detected between peripheral blood, synovial fluid and synovial tissue of JRA patients or between peripheral blood and synovial tissue of RA patients.