1. A technique for isolating and perfusing the rabbit cornea is described, which allowed its thickness to be continuously measured under the microscope. The reversal of thickness of the cold-swollen cornea on perfusion with various solutions at 37 degrees C was studied.2. It was found that only a combination of adenosine and glutathione was able to reliably reverse the thickness to its normal value. This mechanism is sodium, bicarbonate, and oxygen dependent. Inhibitors of glycolysis or electron transport stop the reversal process.3. The findings are consistent with a need for an ATPase but are not capable of distinguishing among several possibilities for its regulation.