ERIC-PCR has been widely used as genomic fingerprinting technology for classification and identification of bacterial isolates. Recently, it has been used by some labs to characterize bacterial mixtures. However, there are still disputes regarding the mechanism of product formation in ERIC-PCR. We cloned and sequenced the 1. 1kb major band of the ERIC-PCR fingerprint of E. coli K-12 strain MG1655, the strain used for whole genome sequencing, and found that the band consisted of 3 different DNA fragments with one fragment the most abundant (93 out of 95 clones, i. e. 97. 89%). Sequence analysis showed that two of the three fragments amplified from a chromosomal region where one ERIC element exist either upstream or downstream, while one fragment amplified from a region where no ERIC element was found. It was thus postulated that ERIC-PCR is not an absolutely random amplified PCR technique, especially when it is applied to those genomes containing ERIC elements.