DNA heterogeneity among strains and isolates of Mycoplasma gallisepticum (MG) was demonstrated with the arbitrarily primed polymerase chain reaction (AP-PCR) method. This method involves three cycles of low-stringency amplification followed by PCR at higher stringency. Reproducible DNA fragments of 25 different MG strains or isolates were generated with three arbitrarily chosen primers. The MG strains or isolates were distinguished according to the banding patterns of their amplified DNA on agarose gels, and the differences were characteristic for specific isolates. This method is rapid, simple, and reproducible, and it can also be used to determine the similarity between isolates of MG from various sources.