Bacterial agglutination(BA) test was used to detect anti-E. coli somatic(O26, O111, O157) antibodies. A total of 355-serum samples were collected from 45 patients were positive by culture for E. coli O157:H7 (group I), from 47 HUS patients without EHEC(group II), from 50 family members of group I and II, from 22 patients of diarrhea with or without blood and from 23 of healthy controls. Sera from 41(91.1%) of the group I, from 34(72.3%) of the group II, from 8(16.0%) of the group III, from 2(33.3%) patients with bloody diarrhea(6 patients) had significant antibody levels(1:160 < or =) to the O157-antigen. Only one patient implicated HUS and without any EHEC had a titer of positive level to the O111-antigen. These sera with significant levels of antibody were revealed at 5th to 6th day of illness, and continued to 45 or more days of illness. Twenty-five(50%) from whom stool specimens were negative by culture for E. coli O157 in the group III had median antibody levels (1:40 approximately 1:80). This group had high antibody levels than two groups of healthy controls and the patients with other pathogen than E. coli O157. These results suggest that high antibody levels members were infected with E. coli O157, and also indicate that BA test of sera from patients with some enteric signs provided valuable for confirmation and diagnosis of the EHEC infection.