We evaluated the efficacy of ciprofloxacin (3 mg/ml) as the sole topical antibiotic used to treat infectious keratitis in 14 patients. We compared the ciprofloxacin-treated group to a retrospective control group of 30 consecutive culture-positive patients treated with conventional therapy in which cefazolin (50 mg/ml) and fortified gentamicin sulfate (9.1 mg/ml) solutions were used. We found no remarkable difference between the control group and the ciprofloxacin-treated group regarding patient age, risk factors, need for hospitalization, and virulence of organism isolated. The average time to healing in culture-positive ciprofloxacin-treated patients was 34 +/- 33 days vs 45 +/- 71 days in the control group and this difference was not statistically significant. The duration of antibiotic therapy in the culture-positive ciprofloxacin-treated group was 27 +/- 15 days vs 33 +/- 50 days in the control group. Four of the 30 control patients required modification of their antibiotic regimen, whereas no ciprofloxacin-treated patient required a change. Ciprofloxacin appears to be an effective single agent in the treatment of ulcerative keratitis.