Mycobacterium w is a non-pathogenic, saprophytic, atypical mycobacterium with the ability to produce macrophage activating factors from lymphocytes of human patients. Prior immunization with heat-killed suspension of Mycobacterium w shows protection against sub-lethal infection with Mycobacterium tuberculosis H37Rv in mice. Heatkilled Mycobacterium w vaccine is manufactured by M/s Cadila Pharmaceuticals, Ahmedabad, India. Combined heatkilled M. w vaccine and multidrug treatment (MDT) revealed clinical, histological and bacteriological improvements in highly bacillated untreated anergic lepromatous cases of leprosy. In healthy contacts of leprosy patients, M. w vaccine has shown lepromin conversion and protection against leprosy. Only a few clinical studies have been carried out using antituberculous treatment with and without M. w vaccine in pulmonary tuberculosis, in which faster sputum conversion and higher cure rate have been observed in M. w group. M. w vaccine has shown potential of Tuberculin conversion in HIV positive subjects. In a study, five monthly doses of M. w vaccine have shown highly significant increase in CD4 count in HIV positive human beings. More clinical trials are needed to confirm beneficial role of M. w vaccine as an immunomodulator in therapy and prevention of tuberculosis, particularly so in multidrug resistant tuberculosis and those with HIV infection.