Ninety-six Escherichia coli strains isolated from cultures of blood specimens taken from both urosepsis patients (n = 48) and non-urosepsis patients (n = 48) were examined for the production of alpha-haemolysin (Hly) and cytotoxic necrotizing factor type 1 (CNF1), the expression of P-fimbriae and mannose-resistant haemagglutination (MRHA). Twenty-seven (56%) of the E. coli strains from urosepsis showed some of the virulence factors investigated, whereas only 15 (31%) of the strains associated with non-urosepsis possessed virulence factors (P < 0.05). By contrast, only 16% (P < 0.001) of the faecal isolates from healthy individuals were virulent. Of the bacteremic E. coli strains, 56 (58%) belonged to one of 8 serogroups (O1, O2, O4, O6, O8, O9, O18 and O83). Virulence factors were concentrated in strains belonging to serogroups O2, O4, O6, O18 and O83. Thus, 23 (72%) of the 32 strains of these 5 groups showed virulence factors, but only 19 (30%) of the 64 strains belong to other serogroups (P < 0.001). The majority of bacteremic O2, O4, O6 and O83 E. coli strains were Hly+CNF1+ and expressed P-fimbriae or MRHA type III, whereas the strains of serogroup O18 were Hly+CNF1- and had P-fimbriae or MRHA type III, whereas the strains of serogroup O18 were Hly+CNF1- and had P-fimbriae. We conclude that strains from urosepsis show more virulence factors than bacteremic strains isolated from non-urosepsis.