To investigate the biochemical changes of the oxidant/antioxidant balance in corneal tissue, and determine the relative corneal endothelial toxicities of the following intracameral antibiotic agents: cefuroxime and vancomycin.The experiment was conducted using New Zealand rabbits. The rabbits were randomly divided into three experimental groups as follows: cefuroxime group (n=10), vancomycin group (n=10), and control group (n=10). Only the right eyes of the rabbits were used in this study. Twenty eyes received injections of 0.1 ml of one of the two antibiotic preparations, and ten control eyes received injections of 0.1 ml of balanced salt solution. Corneal thickness and clarity were measured before, and 3 and 6 h after surgery. The corneal tissues of the rabbits were extracted and homogenized in 2 ml of physiological saline, and kept at -80 degrees C. In the corneal tissue, malondialdehyde (MDA) and total thiol (SH) levels were measured with spectrophotometric methods. Friedman and Kruskal-Wallis tests were used for statistical analysis.Neither cefuroxime nor vancomycin caused corneal thickening and edema at 3 and 6 h after injection, and no anterior chamber reaction was observed in both groups at both measurement times. The level of SH significantly decreased, while the level of MDA significantly increased in the corneal tissue in the cefuroxime group (p=0.001 and p<0.001 respectively). In contrast, no statistically significant change in oxidative-stress parameters was observed in the vancomycin group (p=0.165 and p=0.876 respectively).Corneal endothelial cells are very sensitive to any form of toxic exposure. Using intracameral cefuroxime during the anterior segment surgery may be more toxic on the endothelial tissue in patients with vulnerable corneal endothelium. Because of the definite risk of dosage errors, these agents should be prepared in the hospital pharmacy and not in the operating theatre.