This study was conducted to determine whether the age of the host influences the pathogenesis and therapeutic outcome of drug-treated Pseudomonas aeruginosa keratitis. Young (3- to 5-month-old) and old (1.5- to 3-year-old) rabbits were intrastromally infected with P. aeruginosa ATCC 27853. Sixteen hours later, rabbits in both age subpopulations were divided into three groups and treated topically as follows: group 1, phosphate-buffered saline; group 2, 0.3% ciprofloxacin; and group 3, 0.3% ciprofloxacin, 1.0% prednisolone, and 0.03% flurbiprofen. Drops were given every 15 min for 1 h and then every 30 min for 9 h. At 27 h postinfection, ocular pathology was graded with a slit lamp examination (SLE) scoring system. Aqueous humor was collected for ciprofloxacin quantitation, and corneas were harvested for bacterial enumeration and estimation of polymorphonuclear leukocytes. Young rabbits had more severe inflammation and pathology than old rabbits. At 27 h postinfection, SLE scores and polymorphonuclear leukocyte numbers were significantly higher for young rabbits than old rabbits (P < 0.02), regardless of treatment. Prednisolone and flurbiprofen significantly reduced SLE scores in both age groups (P < 0.03) without affecting the antimicrobial efficacy of ciprofloxacin.