Antigen-specific suppressor cell activity of peripheral blood mononuclear cells was investigated in 20 patients with rheumatoid arthritis (RA) and 16 age- and sex-matched healthy controls. Suppressor cell activity was generated by priming peripheral blood mononuclear cells with high dose antigen (ovalbumin) and adding the washed primed or control (unprimed) cells to autologous, optimally stimulated, target plaque forming cell (PFC) cultures. The ability of the primed cells to interfere with an optimal ovalbumin specific PFC response in the target culture was used as a measure of antigen-specific suppressor cell activity. The results demonstrated that the mean (+/- SE) PFC response of the rheumatoid patients (669 +/- 76 PFC/10(6) cells) was not statistically different from that of the normal controls (722 +/- 83 PFC/10(6) cells), P = 0.1. However, reduced suppressor cell activity was observed in the rheumatoid patients relative to controls (46.4 +/- 4.2% versus 64.6 +/- 2.7% suppression, respectively; P < 0.001). No correlation was demonstrated between suppressor cell activity in rheumatoid patients and disease activity or therapy.