A total of 36 Escherichia coli urinary tract isolates (UTI) of serotype O6, with different combinations of capsule (K) and flagellin (H) antigens, were analysed according to the outer membrane pattern (OMP), serum resistance properties, mannose-resistant hemagglutination using various types of erythrocytes, and also for the genetic presence and the expression of P-fimbriae, S fimbriae/F1C fimbriae, Type 1 fimbriae, aerobactin and hemolysin. Twenty selected strains were further analysed by pulsed field gel electrophoresis (PFGE), elaborating genomic profiles by XbaI cleavage and subsequent Southern hybridization to virulence-associated DNA probes. It could be shown that O6 UTI isolates represent a highly heterogeneous group of strains according to the occurrence and combination of these traits. Relatedness on the genetic and the phenotypic level was found for some of the strains exhibiting the same O:K:H:F serotype. DNA long-range mapping further indicated some interesting features, according to the copy number and the genomic linkage of virulence genes.