Radial keratotomy may cause anatomical damage to the rabbit corneal endothelium. To determine if physiological and functional alterations occur, radial keratotomy was performed on rabbit corneas using eight incisions with sparing of a 3.5-mm central pupillary area. Cornea endothelial membrane permeabilities were determined at various times up to ten weeks following the procedure using simultaneous flux determinations of tritiated inulin and dextran labeled with radioactive carbon on isolated corneas. At all times after radial keratotomy, there was no probable physiologically important change in corneal endothelial permeability to either of the labeled compounds. Fluorophotometry performed in a second group of animals at varying intervals following radial keratotomy showed no probable physiologically important change in endothelial fluorescein permeability. Aqueous humor turnover rate was reduced 16% and 29% at one week and nine to ten weeks, respectively, following radial keratotomy.