We assessed T cell subpopulations using 2-color flow cytometry with phycoerythrin conjugated anti-CD45RA and anti-CD29 and fluorescein conjugated anti-CD4 and anti-CD8 monoclonal antibodies, on peripheral blood lymphocytes from 19 patients with Behçet's disease (BD) and 18 healthy control subjects. The percentage of CD4+ cells was significantly lower in patients with BD (34 +/- 2%) than in control subjects (46 +/- 3%) (p less than 0.001). Among CD4+ cells, the percentage of suppressor-inducer (CD4+CD45RA+) cells was significantly lower in patients with BD (31 +/- 4%) than in control subjects (45 +/- 2%) (p less than 0.01), while the percentages of helper-inducer (CD4+CD29+) cells were similar in patients and controls. The percentage of CD8+ cells was significantly higher in patients with BD (36 +/- 2%) than in control subjects (26 +/- 2%) (p less than 0.001) involving both CD45RA+ and CD29+ subpopulations. Within CD4+ cells, the percentage of suppressor-inducer (CD4+CD45RA+) cells was significantly decreased in patients with active BD (26 +/- 3%) compared with control subjects (45 +/- 2%) (p less than 0.001), whereas in patients with inactive BD the difference was statistically insignificant. Our results suggest that the defective suppressive function in patients with active BD may be related to the decreased suppressor-inducer subpopulation (CD4+CD45RA+).