The interleukin 2 (IL-2) production and responsiveness of peripheral blood lymphocytes from patients with rheumatoid arthritis (RA) with active or inactive disease was compared with that of normal control donors. IL-2 production was assessed using a cellular interleukin assay in which an IL-2 dependent cell line was cocultured with varying numbers of irradiated IL-2 producing lymphocytes from the different donor sources. Cells from patients with active disease showed a significantly different pattern of IL-2 production from that of control or inactive RA patients in that a lower number of cells supported growth of the IL-2 dependent cell line. In one patient this shift in pattern was shown to correlate with change in disease activity. Lymphocyte responsiveness to IL-2 as determined by limiting dilution analysis did not differ significantly between the different groups. The results are consistent with a hyperproduction of IL-2 in RA during active disease.