Nine biopsy specimens from 3 tuberculoid (TT), 1 borderline tuberculoid (BT), 2 borderline (BB), 2 borderline lepromatous (BL), and 1 lepromatous (LL) patients were studied using immunoperoxidase procedures with monoclonal antibodies. In TT patients 4B4+, TCR alpha beta+, CD4+ T cells were dominant in dermal granulomas. In LL patient, dermal granulomas with 4B4+, TCR alpha beta+, CD4+ T cells and 2H4+, TCR alpha beta+, CD4+ T cells also had CD8+ T cells. The proportion of 4B4+ T cells increased in granulomas from LL to TT and 2H4+ T cells proportionately increased from TT to LL. TCR gamma delta+ T cells were detected only in BB and BL patients. However, there is no difference of staining pattern of ICAM-1 or LFA-1 antigen in any type of leprosy. These results indicate that the immunohistochemical pattern of T cells (CD4, CD8, 4B4, 2H4, TCR) may be useful in the diagnosis of the spectrum of leprosy.