The DNA of Mycobacterium tuberculosis is amplified by polymerase chain reaction and we get a specific 158 bp DNA fragment of Mycobacterium tuberculosis.The DNA of Mycobacterium bovis is also amplified,but other thirteen mycobacteria are not.The DNA fragment is recovered and used as a DNA probe,It can hybridizes with DNA of Mycobacterium tuberculosis and Mycobacterium bovis,but not with the DNA of Staphylococcus aureus,Bacillus pyocyaneus and other mycobacteria.This result suggests that the Mycobacterium tuberculosis and Mycobacterium bovis can be detected by PCR and the amplified 158bp DNA fragment can be utilized as a molecular probe. This probe can examine the Mycobacterium tuberculosis and Mycobacterium bovis and distinguish them from other mycobacteria.