Abstract: Using the active E-Rosette test, total E-Rosette test, and acid α-naphthyl acetate esterase(ANAE)cytochemical staining method, the percentage of Ea RFC, Et RFC, ANAE-positive lymphocytes, ANAE-positive Ea RFC and Et RFC in peripheral blood were detected in 76 patients with active leprosy(lepomatous leprosy 46, tuberculoid leprosy 30).The results showed that the percengages of Ea RFC and Et RFC of both groups of leprosy patients were lower than that of the normal individuals.The decrease of ANAE-positive lymphocytes in L leprosy patients was more marked than in T leprosy patients.These findings suggest that active L and T leprosy patients lack mature T lymphocytes and T lymphocytic population with the receptor of sheep erythrocyte in peripheral blood, especially in L patients.Thus, ANAE staining method may be used as a useful approach to determine clinically the state of cell mediated immunity of leprosy patients and to investigate the subpopulation of lymphocytes.