Rabbit corneas were preserved for between 7 and 14 days at + 4 degrees C in a whole eye in synthetic media (T.C. 199 and T.C. Earle) with or without added Dextran. In the absence of Dextran the corneas preserved at + 4 degrees C became thick. This thickening increased with the length of conservation. Dextran limited the hydration of the stroma. Measurement of the variations of corneal thickness during perfusion for 6 hours at 30 degrees C in T.C. Earle could be used as an index of the function of the corneal endothelium. Even after 14 days of preservation at + 4 degrees C the corneal endothelium retained the ability to reduce or prevent hydration during perfusion at 30 degrees C. Histological studies showed good conservation of the cellular structure after 7 days at + 4 degrees C. Pyknosis appeared after 14 days conservation. T.C. 199 preserved endothelial function better than T.C. Earle.