I studied the in vitro effect of three intraocular irrigating solutions--a glutathione bicarbonate Ringer (GBR), a commercially available glucose glutathione bicarbonate solution (BSS Plus), and a citrate-acetate bicarbonate solution (S-MA2)--on the barrier function of the corneal endothelium. The major chemical differences between S-MA2 and GBR or BSS Plus are that S-MA2 does not contain glutathione and phosphate but does contain acetate and citrate. Paired rabbit corneas were perfused separately, and the endothelial permeability (Pac) to carboxyfluorescein was determined. Between the paired corneas perfused with GBR and BSS Plus, there was no significant difference in the Pac, while a significant difference in this factor was seen between the paired corneas perfused with GBR and S-MA2; the figure was about 20% larger for S-MA2. It is suggested that BSS Plus or GBR is less harmful to the endothelial barrier function than S-MA2 and that Pac to carboxyfluorescein can be a useful index in determining the safety of the intraocular irrigating solutions.