A number of bacterial strains (Escherichia coli, Proteus mirabilis and streptococci), obtained from patients with urinary infections, or from vaginal tampons, were assayed in order to evaluate their ability to adhere to uroepithelial cells. We employed, at a comparative purpose, two different methods to eliminate unattached bacteria: the centrifugation technique and the filtration technique. The effect of the pretreatment with subinhibitory concentrations of three chemotherapeutics widely employed in the urological practice (norfloxacin, pipemidic acid and co-trimoxazole) was determined on the strains which demonstrated a good rate of attachment. Growth in the presence of any of the three drugs decreased the adhesive properties of the microorganisms, reducing both the haemagglutination and the yeast aggregation titers of Gram-negative bacteria as well as their adhesiveness. Norfloxacin proved to be the most effective drug in affecting the pathogenicity characteristics of the assayed strains in comparison with the other two chemotherapeutics tested, even if they were also moderately able to inhibit the adhesiveness of the same strains.