Corneal preservation time can be prolonged using chondroitin sulfate (CS) in preservation media and recently a great deal of attention has been focused on evaluating the effectiveness of CS. So far evaluations of the effectiveness of this and other additives have been based on determining the state of the cornea at the end of the preservation period. A more informative determination of the viability of stored corneas can be made by monitoring their physiological parameters throughout the storage period. We have accomplished this by monitoring in vitro the transendothelial electrical potential difference across deepithelialized rabbit corneas. We found that corneas stored in solutions containing basal salts, glucose and CS maintained higher transendothelial potential differences than corneas stored in the same solutions without CS, thus confirming the benefits of using CS for medium-term corneal preservation. The beneficial effects of CS were optimal at the 1% concentration, and were reduced at higher and lower concentrations.