The polymerase chain reaction (PCR) was applied for the identification of field strains of mycobacteria. 28 field strains, cultured on Lowenstein-J medium and identified according to biochemical reactions, were tested in the PCR. The pathological material for culture was collected from different animal species: cow, swine, goat, and poultry. Multiple interspersed negative controls, only reagents without DNA, were included each time a PCR was performed; for the positive control DNA extracted from M. bovis and M. avium of reference strains (ATCC) were used. The PCR was carried out twice, at different times for all field strains examined. The presence and size of each PCR product was determined by electrophoresis on silver-stained 7% acrylamide gel. Two primers: forward primer, 5'-gggTTTgACATgCACAggAC-3' and reverse primer: 5'-TACggXTACCTTgTTACgAC-3' which codify for 16S subunits, were used for PCR amplification of bacteria included in the Mycobacterium genus. A pair of primers, forward primer: 5'-gAACAATCCggAgTTgACAA-3' and reverse primer, 5'-AgCACgCTgTCAATCATgTA-3', which codify for MPB70 protein, were used for amplification of the M. tuberculosis complex. A second method using two further primers codifying for IS986 were then also used to amplify only the M. tuberculosis complex. For the amplification of strains within the M. avium complex, the following sequence of primers were used: forward primer, 5'-gAACgCCCgTTggCTggCCAT-3' and reverse primer, 5'-gCAACACggTCggACAggCCT-3', obtained from a genomic library. With the primers employed, 26 field strains were included in the genus Mycobacterium (92.85%, 18 of which belonged to the M. tuberculosis complex and 2 to the M. avium complex. The Mycobacterium genus was well identified as the M. tuberculosis complex and the M. avium complex, but the PCR was unable to differentiate the species within the complex.