Verotoxin producing Escherichia coli, in particular serotype O157:H7, have been implicated as an important cause of acute gastroenteritis in children. This study was undertaken to determine if E. coli O157:H7 is an important cause of acute gastroenteritis in children in metropolitan Sydney. During the period from October 1990 to September 1991, stools from patients presenting with acute diarrhoea to The Children's Hospital, Camperdown, were examined for the presence of common bacterial pathogens. In addition, stools were grown on sorbitol McConkey agar and sorbitol non-fermenting organisms were serotyped with O157 antiserum by slide agglutination. The isolates were then tested with H7 antisera and investigated for the production of verocytotoxin and other pathogenic markers including plasmid-associated EHEC adhesin and chromosomally encoded attachment-effacement gene. Only two strains (isolated from two different patients, 0.1% of specimens tested) were agglutinated by O157 antiserum and both were non-motile (H-). However, both strains produced verotoxin and expressed other virulence markers, suggesting that they were responsible for the diarrhoea. Both patients experienced mild, self limited gastroenteritis. We conclude that E. coli O157:H7 is an uncommon cause of acute gastroenteritis in Sydney children presenting to a children's hospital.