Two-colour flow cytometry analysis of the peripheral blood T cells in 28 patients with rheumatoid arthritis (RA) and healthy individuals showed a significant decrease in the percentage of the suppressor T cells (Leu 2a + Leu 15+) in severely active disease (5.9 +/- 2.1%) as compared to controls (13.4 +/- 3.8%) and active disease (12.9 +/- 5.9%). A significant adverse correlation was also observed between disease activity (Lansbury's index) and the percentage of suppressor T cells. Activated T cells (Leu 4+ HLA-DR+) were detected in a higher percentage and prevalence in the active group. Two-color immunofluorescence of T cell subsets may provide more accurate information concerning the immune imbalance of RA patients than the conventional single-color analysis.