The stroma and epithelium of human corneas that had been stored in organ culture medium for 10 to 22 days at 37 C were examined by light and electron microscopy. Total corneal thickness was found to be doubled at ten days and there was no further increase even at 22 days. The posterior portion of the stroma was more hydrated than the anterior region. Stromal cells were reduced in number and normal-appearing cells were present only in superficial stroma. The epithelial basement membrane was irregular and thickened. Although the epithelium was reduced to three or four cells in thickness and the intercellular spaces were dilated, the epithelial cells contained normal subcellular organelles and appeared to be viable.