The predominant strain of Escherichia coli, the most frequently associated causative agent of urinary tract infections (UTI), in the rectal flora of patients with UTI has been reported to match the strain associated with the etiologic agent of UTI. Since acquisition of UTI may depend on the immediate surrounding flora of the patient, the chromosomal DNAs of strains of E. coli isolated from 3 patients suffering from recurrent cystitis and asymptomatic bacteriuria were examined by multiple polymerase chain reaction using 6 sets of primers for all the known urovirulence factors and by pulsed-filed gel electrophoresis. Genetically identical or similar strains were continuously isolated from these patients and each strain carried the identical urovirulence factors. The findings strongly supported the previous notion that the acquisition of UTI is dependent upon the occurrence of the strain carrying the urovirulence factors in patients or in the environment.