Two groups of Escherichia coli were assayed to evaluate hydrophobic characters and the secretion of enzymes and cytotoxic factors. Group 1 included strains isolated from the urine of patients with lower urinary tract infection (UTI) and group 2 included strains from the same sample of asymptomatic subjects. The bacterial hydrophobicity was similar in the two groups and related to their adhesion to plastic surfaces, while both cytotoxic factors (demonstrated using a microscopic and a spectrophotometric technique) and hydrolysing enymes were secreted more by the first group of E. coli. The superior production of these factors may be important in the pathogenesis and in the development of symptomatic UTI infections.