Four hundred and forty-nine strains isolated from patients with diarrhoea and belonging to 13 enteropathogenic Escherichia coli (EPEC) O serogroups were tested with a DNA probe for the EPEC adherence factor (EAF). Positive results were obtained with only 36 strains; they belonged to 10 O serogroups and flagellar typing showed they were usually of the "classical" EPEC serotypes. Thirty-four of the 36 EAF-positive strains showed localised adhesion to HEp-2 cells. The two remaining strains, of serotypes O114:H2 and O127:H4, showed low level or no adhesion to HEp-2 cells. No colonies hybridising with the EAF probe were identified in cultures from 115 faecal specimens from healthy children. Sixteen of the 449 strains hybridised with one or both probes for the Vero cytotoxin genes VT1 and VT2; 15 of the 16 strains belonged to serogroups O26 and O128. None of the strains hybridised with both the EAF and VT gene probes. These studies show that the great majority of strains belonging to EPEC O serogroups do not possess the EPEC adherence factor or carry VT genes.