Tuberculosis and leprosy, caused by Mycobacterium tuberculosis and M. leprae respectively, remain major problems in the developing world. Mycobacteria also causes the opportunistic infection of AIDS patients. BCG, an attenuated strain derived from virulent bovine tubercle bacilli(M bovis), is one of the most widely used human vaccine against tuberculosis and has been proposed as a host for the construction of recombinant live vaccines expressing novel protective epitopes. BCG offers some unique advantages for developing such a multivaccine vehicle, including a long record of use in humans with a low incidence of serious complications, stability in the field, long-lived immune responses with a single-dose usage and a low cost to produce. With the development of methods for introducing DNA into mycobacteria, and the propagation and expression of foreign genes, BCG may well take on a fresh release of life, the old stager re-emerging as a star performer.