These immunopathogenesis studies of leprosy have provided new insight into the immune response to M leprae at the site of disease activity, the skin lesions. The study of leprosy provides a model for studying the immune response to foreign pathogens as well as the immunopathologic study of skin lesions. Further developments in immunology and molecular biology will increase our ability to dissect such immune mechanisms. For example, the advent of the polymerase chain reaction will allow for a more complete elucidation of the cytokines in inflammatory skin lesions.