Immune responsiveness to Mycobacterium leprae was studied, by the method of leucocyte migration inhibition, in ninety healthy adults allocated into four groups according to previous contact with leprosy patients. Groups working or living in close relationship with leprosy patients responded significantly more strongly to M. leprae than a group without such contact. With a selected concentration of M. leprae 71.2 per cent of medical attendants dealing with leprosy patients, 22.2 per cent of administrative staff of a leprosy hospital, and 50 per cent of household contacts of leprosy patients showed migration indices
