T lymphocytes from patients with lepromatous leprosy are anergic to M. leprae antigens. The mechanisms which induce and maintain this antigen specific T cell unresponsiveness in lepromatous leprosy have been the subject of intensive research. Recent insights from work on T cell recognition of antigen, cytokines, and T cell subsets have considerably enhanced the understanding of the immunopathology of lepromatous leprosy.