Purpose: To investigate the aqueous penetration of 3 commercially available ophthalmic fluoroquinolones. Design:Prospective, double- masked, clinical study. Participants: Fiftytwo eyes of 52 patients. Intervention: Fifty- two patients undergoing cataract surgery were given preoperative topical gatifloxacin 0.3% (Zymar), moxifloxacin 0.5% (Vigamox), or ciprofloxacin 0.3% (Ciloxan). The patients were instructed to use their antibiotic drops 4 times a day for 3 days before surgery. On the day of surgery, patients were given their assigned antibiotic every 15 minutes for 3 doses, 1 hour before their procedure. At the time of surgery, 0.1 ml of aqueous fluid was aspirated from the anterior chamber with an air cannula needle attached to a tuberculin syringe. The aspirate was immediately stored at- 70° C. Main Outcome Measure: Fluoroquinolone concentrations were determined by reverse- phase high- pressure liquid chromatography assay technique with ultraviolet detection at a wavelength of 275 nm. Results: Mean aqueous concentration of gatifloxacin in 16 eyes was 0.63 μ g/ml (standard deviation [SD], 0.30),moxifloxacin in 14 eyeswas 1.31 μ g/ml (SD, 0.46), and the mean concentration of ciprofloxacin in 22 eyes was 0.15 μ g/ml (SD, 0.11). Conclusions: Bothmoxifloxacin (P< 0.001) and gatifloxacin (P< 0.005) penetrated the aqueous humor at significantly higher levels than ciprofloxacin. Moxifloxacin penetrated into the aqueous humor at significantly higher levels than gatifloxacin (P< 0.05). The anterior chamber levels of moxifloxacin and gatifloxacin may be due to the difference in antibiotic concentration. Purpose: To investigate the aqueous penetration of 3 commercially available ophthalmic fluoroquinolones. Design: Prospective, double-masked, clinical study. Participants: Fiftytwo eyes of 52 patients. Intervention: Fifty- two patients undergoing cataract surgery were given preoperative topical gatifloxacin 0.3% ( Zymar), moxifloxacin 0.5% (Vigamox), or ciprofloxacin 0.3% (Ciloxan). The patients were instructed to use their antibiotic drops 4 times a day for 3 days before surgery. On the day of surgery, patients were given their assigned antibiotic every At the time of surgery, 0.1 ml of aqueous fluid was aspirated from the anterior chamber with an air cannula needle attached to a tuberculin syringe. The aspirate was immediately stored at- 70 ° C Main Outcome Measure: Fluoroquinolone concentrations were determined by reverse-phase high- pressure liquid chromatography assay technique with ultraviolet detection at a wavelength of 275 Results: Mean aqueous concentration of gatifloxacin in 16 eyes was 0.63 μg / ml (standard deviation [SD], 0.30), moxifloxacin in 14 eyes was 1.31 μg / ml (SD, 0.46), and the mean concentration of ciprofloxacin in Moods of both eyes were significantly higher than that of ciprofloxacin (P <0.005). 22 eyes was 0.15 μg / ml (SD, 0.11). Conclusions: Bothmoxifloxacin (P <0.001) and gatifloxacin than gatifloxacin (P <0.05). The anterior chamber levels of moxifloxacin and gatifloxacin may be due to the difference in antibiotic concentration.