Patients with leprosy may be classified into two clinical and histopathologic categories. At one end of the spectrum, patients with tuberculoid leprosy have few skin lesions in which organisms can rarely be identified. At the other end of the spectrum, patients with lepromatous leprosy have numerous skin lesions containing myriad bacilli. Because immunologic resistance is associated with this spectrum, the study of leprosy provides a unique opportunity to gain insight into immunoregulatory mechanisms in man. In addition, serodiagnosis to identify early cases and prevention by vaccination are areas of active research. For patient care, a network of Regional Hansen's Disease Centers has been established under the sponsorship of the National Program for Hansen's Disease, Carville, LA. Because the patients are often poor, their receipt of care and medication without cost helps to ameliorate at least one of the burdens imposed by this potentially devastating illness. The program central office may be called at 800-642-2477.