In this study, effects of efflux pump inhibitors, phe-arg-beta-naphthylamide (MC-207,110), verapamil, omeprazole and lansoprazole, on ciprofloxacin minimal inhibitory concentrations (MIC) against Escherichia coli clinical isolates with high level fluoroquinolone (FQ) resistance, were evaluated. Fourteen FQ resistant clinical isolates of E. coli isolated from urine samples and identified by BD BBL CRYSTAL Identification Systems Enteric/Nonfermenter ID kit (Becton Dickinson and Company Sparks, USA) were tested. In order to investigate the effects of inhibitory agents, MIC values were determined by broth microdilution method in the absence or presence of 20 microg/ml MC-207,110, verapamil, omeprazole and lansoprazole. All 14 clinical isolates were resistant to ciprofloxacin (MIC range; 16-512 microg/ml). No difference was observed on ciprofloxacin MIC values in the presence of 20 microg/ml omeprazole, whereas MIC values were decreased 2 folds in 2 isolates in the presence of verapamil and lansoprazole, 2 folds in 6 isolates and 4 folds in 2 isolates in the presence of MC-207,110. In conclusion, we observed that there were no effects of the compounds used in our study, on ciprofloxacin resistance of E. coli clinical isolates.