Several aspects of interleukin-2 (IL-2) generation and function were studied employing mononuclear cells from synovial fluid (SF), synovial tissue (ST) and peripheral blood (PB) of patients with rheumatoid arthritis (RA). Decreased PHA stimulated IL-2 production by lymphocytes from rheumatoid ST, SF (P less than 0.02), and PB (P less than 0.01) was observed when compared to normal blood and SF of patients with gout. The proliferative response of rheumatoid lymphocyte blasts exposed to exogenous IL-2 was also defective (P less than 0.05-0.001). This defect was greater in SF than in rheumatoid PB (P less than 0.05-0.001). In addition to the proliferative response, the effect of IL-2 on interferon-gamma (IFN-gamma) production was also examined. Rheumatoid lymphocytes from both PB and SF produced less IFN-gamma after overnight treatment with IL-2 than did normal PB lymphocytes. This decreased IFN-gamma induction was discordant with the excellent enhancement by IL-2 of natural killer activity. Removal of adherent cells in synovial fluid did not correct this deficit. Abnormalities in the biology of IL-2 and IFN-gamma suggest that impaired T cell function could contribute to the immunopathogenesis of RA.