Metabolic and biochemical changes of the corneal epithelium and endothelium were studied in experimental diabetic animal models. Ocular redox fluorometry was used to noninvasively determine tissue reduction-oxidation (redox) changes in organ cultured rabbit corneas incubated in high glucose concentration media, alloxan-induced diabetic rabbits, and nonobese diabetic mice. The ratio of autofluorescence from reduced pyridine nucleotide to oxidized flavoproteins (PN/Fp) was used as the indicator of the redox state. Chemical assays for NADH and NAD+ were performed on in vitro materials. Analysis of corneal endothelial morphology using specular microscopy was performed to study possible correlations with metabolic changes. Both the PN/Fp and NADH/NAD+ ratios increased in the corneal endothelium under all experimental conditions. Changes in redox state were not observed in the corneal epithelium in any of the models. Morphologic analysis of the corneal endothelium revealed no significant changes. These results indicate that redox changes occur in the diabetic corneal endothelium, but not the corneal epithelium. Ocular redox fluorometry is capable of detecting changes in the corneal endothelial redox state noninvasively.