Abstract: The T cell subsets in the peripheral blood were determined by using monoclonal antibody and immunoperoxidase technique in patients with Behcet's disease (BD) and compared with normals. The results revealed that there were no obvioiu changes of the percentage of OKT3⁺ cells and Ia⁺ cells in patients with BD as compared with normals. The percentage of Leu3a⁺ cells decreased. The percentage of Leu-2a⁺ cells increased. The ratio of Leu3a/Leu2a decreased significantly. There were, however, no obvious changes of T cell subsets between the active stage and inactive stage, complete type and incomplete type of BD.