Chronic bacteriuria is a common occurrence among spinal-cord injury patients and others with neuropathic bladders. If bacteria are present in the urinary tract, the patient may develop symptoms of infection or remain asymptomatic. We have compared virulence properties of 28 Escherichia coli isolates from patients with symptomatic urinary tract infections (UTI) and 29 E. coli isolates from patients with asymptomatic bacteriuria (ABU). Bacteria from patients with symptomatic UTI were more likely to be hemolytic than isolates from patients with ABU (P = 0.05) or fecal isolates obtained from healthy volunteers (P < 0.001). Bacteria from patients with symptomatic UTI were also more likely than strains isolated from patients with ABU (P = 0.08) or fecal strains (P < 0.001) to exhibit D-mannose-resistant hemagglutination of human erythrocytes. The results suggest that E. coli isolates from nonimmunocompromised patients who require intermittent catheterization and who develop symptomatic UTI may be distinguished from bacteria recovered from patients who remain asymptomatic and possibly from normal fecal E. coli.