In the present study, we aimed at comparing the efficacies of intravitreal piperacillin/tazobactam and ceftazidime applications in the treatment of experimental Pseudomonas aeruginosa endophthalmitis in rabbit eyes. Twenty-four New Zealand white albino rabbits were divided into three groups (n=8 in each), and the right eyes received 0.1 ml intravitreal injections of P. aeruginosa suspension. The left eyes served as uninfected control and were injected with 0.1 ml of saline solution. The right eyes of rabbits in group 1 were treated with intravitreal injection of 250 mu g/0.1 ml piperacillin/tazobactam 24 hr after intravitreal inoculation of P. aeruginosa, whereas group 2 eyes received intravitreal 1 mg/O (.) 1 ml ceftazidime. Group 3 eyes received no treatment and served as infected controls. Clinical, microbiological and histopathological evaluations of the eyes in each group were performed on the 1st, 3rd, and 6th day after the inoculation of P. aeruginosa. The mean clinical scores of each group were similar at the first day after P. aeruginosa inoculation (P > 0.05). At the 6th day, there was no statistically significant difference in mean clinical scores between group 1 and 2, but mean clinical score of group 3 was significantly higher (P < 0.001). Microbiological analysis and histopathological scoring demonstrated no statistically significant difference between group 1 and 2 (for each, P > 0.05). Group 3 eyes had a significantly more CFU/ml and higher histopathological score (for each, P < 0.001). In conclusion, intravitreal application of 250 mu g/0.1 ml piperacillin/tazobactam seems to be effective in the treatment of P. aeruginosa endophthalmitis in rabbits, but is not superior to intravitreal ceftazidime application. Therefore, intravitreal piperacillin/tazobactam may be a useful alternative to ceftazidime for pseudomonal endophthalmitis. (c) 2004 Elsevier Ltd. All rights reserved.