The electrophoretic profiles of outer membrane proteins and lipopolysaccharide of sixty-five enterotoxigenic Escherichia coli of different serotypes and virulence-associated factors, toxin and colonization factors were determined. A close relationship between serotype and outer membrane protein and lipopolysaccharide patterns could be observed. No correlation could be found between the electrophoretic profiles and the expression of virulence-associated factors. The observed homogeneity of outer membrane protein and lipopolysaccharide profiles suggested the presence of only a few clones in the samples studied, and supported the use of outer membrane protein and lipopolysaccharide analysis as a useful epidemiological tool in the characterization of enterotoxigenic Escherichia coli isolates.