Leukocyte subsets present in the granulomatous response produced after the inoculation of a mixture of Mycobacterium leprae and BCG in lepromatous leprosy patients Were Characterized in situ using monoclonal antibodies and an immunoperoxidase technique. The granuloma produced after M. leprae -BCG Showed a distribution like pattern to tuberculoid granulomas . T lymphocytes bearing the CD8 phenotype (T cytotoxic / suppressor) Were sequestered to the periphery of the epithelioid tubercles and T helper-inducer CD4 + lymphocytes infiltrate the Were distributed THROUGHOUT. Langerhans cells CD1 + Were Increased in the epidermis, dermis and in They Were localized mainly in the mantle surrounding the granuloma . Most of the dermal infiltrate produced after the inoculation or M. leprae -BCG expresses the HLA antigen -DR. Similarly, keratinocytes Were MOST Also positive to this MHC antigen. The granulomatous response to BCG was similar to the inoculation of a mixture of M. leprae -BCG, however acid-fast bacilla Were still present. The inoculation of M. leprae produced by macrophage granuloma With No clearing of the bacilla Which Resembles the lepromatous leprosy granuloma.