The effect of quinolones ciprofloxacin (CPX), norfloxacin (NOR), pefloxacin (PFX), and ofloxacin (OFX) on the adherence and on the preformed biofilms of P. aeruginosa to vascular catheters (VC) was studied in an in-vitro model using modified Robbins device. The presence of adherent viable bacteria was determined by culture on blood agar plates and quantitation of CFUS after dislodging the adherent cells into normal saline by sonication. The glycocalyx formation and adherence were also studied by scanning electron microscopy (SEM). In the presence of subìnhibitory concentration of quinolones (0.5-, 0.25-, & 0.125-MIC) no or slight growth was observed around the segments and the number of the adherent cells was reduced to 21-23%, 40-46%, and 55-70% of the controls, respectively. Significant reduction in the glycocalyx formation and adherent bacteria was observed by SEM. In a separate set of experiments, the catheter segments were precolonized with P. aeruginosa for 24h and exposed to the quinolones in concentration 50 µg/ml (5 MIC) and 100 µg/ml for 2hrs. Slight or no growth was observed around the treated segments, while a heavy growth was reduced to less than 5% of the controls in VC treated with 50µg/ml of the quinolones and complete removal of the adherent cells was achieved with 100 µg/ml. By SEM a very small amount of glycocalyx and a few scattered microcolonies were seen after treatment with 50 µg/ml, no organisms were seen in the presence of 100 µg/ml. These data show that the subinhibitory concentrations of CPX, NOR, PFX, and OFX sgnificantly inhibit the adherence of P. aeruginosa to vascular catheters. Clinically achievable concentration of quinolones were able to eradicate the preformed biofilm on the VC.