Twenty-one patients with definite or classical rheumatoid arthritis (RA) were investigated for their suppressor cell activity by a Concanavalin A suppressor cell assay. Two patients had active disease, 9 moderately active disease, and 10 inactive disease according to clinical and laboratory parameters. A mean of 41 +/- 7% suppression was observed in RA patients as compared to 63 +/- 7% suppression observed in 10 healthy age and sex matched controls. No significant difference was observed between patients with moderately active or active disease (39 +/- 9%) and patients with inactive RA (43 +/- 10%). However, a borderline statistical significance (p = 0.05) was seen between controls and patients with moderately active or active RA. Use of autologous serum instead of AB serum for suppressor cell induction had no significant effect, although an increase of the mean suppression was noted (58 +/- 6%) in patient's group. No correlations existed between suppressor cell activity and presence of circulating Clq-binding immune complexes (solid-phase Clq assay), rheumatoid factor (Waaler-Rose test) or antinuclear antibodies (indirect immunofluorescence). This study indicates that lymphocytes of patients with inactive RA exert normal suppressor cell activity. It may well be that patients with active rheumatoid arthritis have decreased suppressor cell function. This will be assessed in a larger group of patients with active disease.