Strains of Escherichia coli from upper and lower urinary-tract infections and from faeces were examined: for their ability to adhere to urinary-tract epithelial cells, buccal epithelial cells and HeLa cells; to invade HeLa cells; to cause keratoconjunctivitis in the guinea-pig eye (Serény test) and for the presence of type-I fimbriae. Strains from infections of the upper and lower urinary tract more commonly adhered and invaded than did faecal strains, but none of the strains gave a positive result in the Serény test. Adhesive strains adhered to best to urinary epithelial cells, less well to buccal epithelial cells and poorly to HeLa cells. All adhesive strains were fimbriate, but not all fimbriate strains adhered.