Rabbit corneas were injected intrastromally withPseudomonas aeruginosa. Sixteen hours after injection, the rabbits were divided randomly into four treatment groups (3 rabbits/6 eyes per group: 1, ciprofloxacin and prednisolone; 2, ciprofloxacin only; 3, prednisolone only; 4, untreated. Ocular signs of inflammation were graded in a masked fashion by slit lamp examination before injection and 16 and 27 hours after injection. Slit lamp examination scores were significantly lower in eyes receiving ciprofloxacin and prednisolone or prednisolone alone, compared with scores in untreated eyes. Slit lamp examination scores were not significantly lower in eyes receiving ciprofloxacin alone, compared with untreated controls. The numbers of viable bacteria in the corneas treated with ciprofloxacin and in the corneas treated with ciprofloxacin and prednisolone were similar and were significantly less (P<0.0001) than those in untreated corneas, indicating that the presence of the steroid did not interfere with the bactericidal action of ciprofloxacin.