Six hundred and seventy-five Escherichia coli isolates obtained from 225 diarrhoeal children less than five years of age were tested for adherence to HeLa cells and for hybridisation with DNA probes for genes conferring aggregative adherence (AggA), localised adherence (LA) and diffuse adherence (DA) to assess the usefulness of a recently developed DNA probe for AggA of enteroaggregative E. coli (EAggEC). The strains were further analysed with the DNA probes for heat--labile enterotoxin (LT), heat--stable enterotoxin (ST), Shiga--like toxins (SLT I and SLT II) and for enteroinvasiveness and adherent strains were all negative for these properties. The HeLa cell assay and DNA probe assays showed excellent agreement in identifying LA and DA positive isolates. However, significant disparities occurred in the case of AggA positive isolates, and the DNA probe failed to identify 31.9% (15 of 47) of the EAggEC identified by the HeLa cell adherence assay. The failure of the DNA probe to identify all the EAggEC indicated that there may be a high degree of genetic heterogeneity for the expression of AggA, and development of more DNA probes is necessary to detect all the possible genetic variants of EAggEC.