The proposed studies center on determining the limiting characteristics of the endothelial transport system of the rabbit cornea. Studies on the isolated cornea will use a variety of environmental changes (e.g. chloride concentration) and inhibitors (e.g. ouabain, amiloride) to examine the regulatory mechanisms underlying the bicarbonate transport system and any co- or counter-ion associated with the net bicarbonate transfer. Continued studies will be made on the effects of photodynamic activation of dye solutions producing free radical oxygen on the corneal endothelium and its modification using fatty acids. Drug effects, as they influence the corneal epithelium and endothelium, will be studied, both from a functional and anatomical viewpoint.