The limitations of the current approach to leprosy control through mass treatment of patients are well recognized. The long incubation period of the disease, the insidious onset, the chronic course, and the need for prolonged treatment have made control a formidable task. The recent years have seen tremendous progress in the field of immunology of leprosy, and the availability of large quantities of Mycobacterium leprae, grown in the nine-banded armadillo, has given impetus to the search for a vaccine specific for leprosy. Methods for production and purification of M. leprae have now been developed and the resulting preparation has been shown to produce good delayed-type hypersensitivity in mice and guinea pigs.Small-scale studies in human subjects have shown that preparations of M. leprae and BCG can induce cell-mediated immunity in Mitsuda-negative patients and contacts. It is now appropriate to consider field trials of vaccine preparations in selected groups before moving on to large-scale trials in different populations.