The clonal relationship of thirty E. coli strains of 0 antigen serotype 06 isolated from human, dog, pig or cow infections were investigated. Two main clones with serotypes 06:H1 or 06:H31, H− were identified. Isolates from humans, dogs, pigs and cows were found in both clones, indicating that animals are a possible source for human extraintestinal Escherichia coli strains. Two human ETEC (06:H16) and two pig isolates (06:H10) were not related to the 06:H1 or 06:H31, H−E. coli clones.