The frequency of electrophoretic types B1 (fast mobilities) and B2 (slow mobilities) of carboxylesterase B, and alpha-haemolysin and mannose-resistant haemagglutinin (MRHA) production were compared in 705 strains of Escherichia coli isolated from cases of septicaemia, urinary tract infection (UTI) and other extra-intestinal infections from different geographical origins, in particular France, America (USA and Canada) and Oceania (Australia and New Zealand). In all groups of strains, whether classified according to their clinical or their geographical origin, electrophoretic type B2 was phenotypically linked with alpha-haemolysin and MRHA production. Haemolytic type B2 strains were isolated more frequently from France and Oceania than America whereas the proportions demonstrating production of MRHA were similar among the three groups. Type B2 strains were more frequently isolated from UTI and other infections than from septicaemia. This is attributed to the high frequency of immunocompromised subjects in the septicaemia group. Our results establish the suitability of using the type B2 of carboxylesterase B as a molecular marker for highly pathogenic E. coli strains implicated in extra-intestinal infections in man.