We determined whether various Escherichia coli O157:H7 isolates could be detected using a probe, an alanine racemase gene (dadX) fragment, specific to E. coil. One hundred strains of E. coil O157:H7 were isolated from fecal samples of healthy cattles and human patients with diarrhea and from a leg of beef. Most isolates (95 strains) produced both verocytotoxin 1 (VT1, Shiga-like toxin I) and verocytotoxin 2 (VT2, Shiga-like toxin II), whereas four isolates produced only VT2. Although neither VT1 nor VT2 was detected in one isolate under the conditions used, the VT2 gene was detected. When all of the isolates were analyzed by a DNA hybridization method involving the use of the probe, positive signals were obtained from all isolates. The DNA hybridization method used for detection of E. coil is considered to detect various E. coli O157:H7 isolates which differ in the types of verocytotoxin they produce.