The occurrence of coliform bacilli carrying resistance-transfer factors (R factors) in children was studied. The frequency of R+ coliform bacilli as causes of urinary-tract infection acquired outside hospital was found to be similar to that in adults from the same geographical area and in the same years. The frequency of R+ coliform bacilli in the faeces in our children was also similar to that in the adult population, and oral chemotherapy produced similar changes in the faecal flora.