A random amplified polymorphic DNA(RAPD) fingerprinting method has been developed to differentiate Enterohemorrhagic Escherichia coli(EHEC) O157:H7 isolates. This method uses an oligonucleotide of arbitrarily chosen sequence to prime DNA synthesis from pairs of sites to which it is matched or practically matched and results in strain-specific arrays of DNA products. By the RAPD analysis using A07(5'-TGCCTCGCACCA-3'), EHEC strains tested in this study were found to be divided into 5 groups. The RAPD arrays among 5EHEC clinical isolates from a single outbreak were identical from each other, and different from other origin. The data indicate that the RAPD method is feasible for investigating the source of an outbreak associated with EHEC O157:H7 infection.