Human corneas were preserved up to 40 days in a modified tissue culture medium at 31 degrees C. The corneal endothelium was examined by light microscopy before and after culture. After staining with trypan-blue the number of dead cells was counted and by swelling of the intercellular borders in a 1.8 per cent sucrose solution the cellular mosaic was observed. A loss of endothelial cells was found varying from 0-30 per cent. During culture the stroma increased considerably in thickness. Prior to transplantation the cornea was thinned during 24 h in culture medium containing 5 per cent Dextran T500. The combination of the organ culture procedure and the evaluation of the endothelium enables preservation of human corneas for at least 30 days. In addition the quality of the endothelium is guaranteed and the transport of corneas can be carried out at room temperature.