Small skin biopsies (4 mm) are required to diagnose the stages of leprosy and cutaneous Leishmaniasis and ascertain the frequency and number of intracellular bacilli and parasites. Patients with lepromatous leprosy have only a few T lymphocytes (of the T8 suppressor subset) in their skin lesions associated with bacilli-laden macrophages. They lack appreciable number of T4 helper cells in the skin and have reduced numbers of epidermal Langerhans' cells. In addition, their circulating lymphocytes fail to make the macrophage activating lymphokine--interferon - when challenged with M. leprae. They are supposedly responsive to antigens other than M. leprae such as PPD - which in presensitized normal individuals leads to extensive emigration of helper cells in the local delayed reaction. We wish to examine the delayed hypersensitivity reactions to PPD in leprosy patients. Will helper T4 cells enter the lesion? Will lymphokine producing helper cells activate bacilli-laden macrophages? Is the defect of lepromatous leprosy a general problem of cell emigration or are helper T cells selectively excluded? Biopsies of these lesions will be examined with fluorescent, monoclonal antibody reagents and by transmission electron microscopy to identify and enumerate the types of emigrating cells. These studies have general application to all forms of cell mediated immunity in man. To confirm that the responses obtained in leprosy patients are representative of the normal DTH response normal volunteers will be examined for their delayed hypersensitivity reactions to PPD, and the local response compared to that observed in leprosy patients.