We studied T cell subpopulations and their immunoregulatory circuits in the peripheral blood of 16 patients with rheumatoid arthritis (RA) who were receiving no medications that might interfere with the results. We found normal T cells with receptors for the Fc portion of IgG or IgM as well as autologous rosette-forming T cells (Tar cells), a subpopulation of T cells we have found to have the properties of human post-thymic precursors. We also found that peripheral blood cells of RA patients have normal concanavalin A-induced or spontaneously-expanded suppressor cell functions. Also normal were the characteristic functions of the Tar cells; feedback inhibition and the generation of suppression. The normal state of these T cell subpopulations and immunoregulatory circuits in the peripheral blood of patients with RA contrasts with their various abnormalities in other connective tissue diseases. This may either mean that the immunoregulatory aberration in RA involves primarily B cells, or, if it involves T cells, that it does so primarily in the synovial membrane.