Mycobacterial polypeptides from 2 kDa to 14 kDa may be involved in host response to infection and be useful for new diagnostics and vaccines. Tris-tricine SDS-polyacrylamide gel electrophoresis separation of proteins in tuberculin purified protein derivative (PPD) and in 6-8-week culture filtrates of Mycobacterium tuberculosis, Mycobacterium bovis BCG, and other Mycobacterium species demonstrated as many as 10 low molecular mass bands. Common and distinct bands were observed among different species and PPD. These low molecular mass culture filtrate proteins may represent potential diagnostic reagents and vaccines for Mycobacterium tuberculosis.