Lymphocytes were eluted from the synovial tissue of seventeen patients with rheumatoid arthritis (RA) and one with ankylosing spondylitis. In eight of these patients immunoglobulin production by synovial lymphocytes in the presence and absence of pokeweed mitogen was studied. In nine patients T lymphocytes were isolated from the eluted cells, and the T helper and suppressor cell functions were evaluated in an allogeneic co-culture system. Peripheral blood lymphocytes (PBL) from twenty-eight normal donors were also studied for comparison. Immunoglobulin produced by synovial lymphocytes was higher than in PBL of normal donors. However, the stimulation index of synovial tissue lymphocytes was lower. Most of the normal donors had suppressor cell activity in their peripheral blood, whereas in synovial tissue lymphocytes a statistically significant number of patients did not have any suppressor cell activity. In contrast, the synovial tissue lymphocytes showed helper activity not differing significantly from that of the T lymphocytes from peripheral blood of normal individuals.