OBJECTIVE: Cell surface molecules can be shed by activated T lymphocytes and measured in serum to assess in vivo T cell activation. To evaluate the relationship between these serum markers and disease activity in rheumatoid arthritis (RA), we determined levels of soluble interleukin 2 receptor (sIL-2R), CD4 (sCD4), and CD8 (sCD8) in sera from a well characterized group of 26 patients with active RA treated with a nonsteroidal antiinflammatory drug (NSAID) alone. METHODS: A retrospective, blinded determination of sIL-2R, sCD4, and sCD8 levels in serum samples from patients with early, active RA participating in 2 trials of NSAID therapy. Commercially available enzyme linked immunosorbent assays were employed. Data analysis included nonparametric techniques and correction for multiple comparisons. RESULTS: The patients with RA had significantly elevated levels of sIL-2R at baseline compared with age matched healthy controls. During NSAID therapy, mean sIL-2R levels among responders decreased to lower levels while nonresponder levels increased, although these trends did not reach statistical significance. Patients with RA did not differ from controls in baseline measures of serum sCD4 or sCD8 levels. Moreover, the serum sIL-2R, sCD4, and sCD8 levels among patients did not vary significantly from their baseline measures during NSAID therapy, irrespective of response. CONCLUSION: Our results suggest that elevated levels of serum sIL-2R in early RA likely reflect generalized immune system activation, not always associated with elevated serum sCD4 or sCD8 levels or varying with other measures of disease activity in RA.