The protective effects of oxidized glutathione (GSSG) and reduced glutathione (GSH) in the irrigating solution based on BSS plus composition (Santen, Osaka, Japan), which is without GSSG (glutathione-free control solution) were compared on rabbit corneal endothelial barrier function. Corneal barrier function was evaluated by determining the effects of GSSG and GSH on carboxyfluorescein permeability (Pac). In a solution containing 0.3 mM GSSG (BSS plus), the Pacwas significantly inferior to that of its paired glutathione-free control solution. With 0.6 mM GSH, the Pacwas not different from that of its paired glutathione-free control solution. The Pacof the endothelium with 0.3 mM GSSG was significantly inferior to that of paired corneas exposed isolated to 0.6 mM GSH. These results show that the barrier function of the rabbit corneal endothelium is better maintained by supplementing the perfusion solution with 0.3 mM GSSG rather than 0.6 mM GSH.