Mycobacteria continue to be responsible for diseases in human and domestic animals worldwide. Though the improved living standards have been accompanied by a progressive decline in cases of tuberculosis, the incidences of disease have remained high in most of the developing countries. A battery of monoclonal antibodies specific mycobacterial antigens would provide a useful tool for rapid diagnosis of mycobacterial diseases. Six monoclonal antibodies to perchloric acid soluble, ethanol extractable and heat stable antigen of Mycobacterium tuberculosis were produced. Immunoglobulin isotypes of monoclonal antibodies were all IgM type. By Western blotting, the monoclonal antibody showed a positive reaction with 58 kDa Mycobacterium tuberculosis protein. Besides Mycobacterium tuberculosis, this monoclonal antibody was reacted with Mycobacterium bovis BCG, Mycobacterium gordonae, Mycobacterium intracellulare, Mycobacterium scroflaceum, but not with Staphylococcus aureus and E.coli.