The majority of synovial fluids from 29 rheumatoid arthritis patients were strongly attractive for normal blood lymphocytes judged by assays of polarization and collagen gel invasion. While rheumatoid synovial fluids contained IL-15, IL-8, monocyte chemotactic protein-1 (MCP-1) and macrophage inflammatory protein-1 alpha (MIP-1 alpha) at levels sufficient to attract lymphocytes, inhibition of the activity of any single cytokine using specific antibody did not abolish the activity of the fluid. However combinations of anti-cytokine antibodies used together (anti-IL-15+anti-MCP-1; anti-IL-8+anti-MCP-1 or +anti-MIP-1 alpha) inhibited most of the activity, suggesting that attraction of lymphocytes by the fluids is due to a combination of attractants. Blood lymphocytes required activation by overnight culture to respond optimally, while rheumatoid synovial tissue lymphocytes responded to synovial fluids without a requirement for a period of culture. Lymphocytes derived from rheumatoid synovial fluids were poorly responsive to locomotor stimulants. Most of the responding cells from blood mononuclear cell fractions were T lymphocytes of the CD45RO isotype. Incubation in the presence of cyclosporin A or corticosteroids inhibited the response of lymphocytes to the fluids, but the presence of non-steroidal anti-inflammatory drugs (NSAIDs) and other agents used in therapy of the patients from whom the fluids were taken had no inhibitory effect.