Sixty-three penetrating keratoplasties were performed in 63 patients using donor corneas stored by 37 C organ culture incubation for an average of 13 days (range 2 to 35 days). No grafts failed before four weeks, except one which was stored at 4 C for 48 hours prior to transplantation, indicating that endothelial viability is maintained when proper storage conditions are maintained. Sixteen grafts have failed as a result of factors other than the storage method. This clinical study confirms our previous laboratory conclusions that 37 C OC incubation up to 35 days improves the quality of donor endothelium compared with other methods of storage, and it represents a significant advance in corneal preservation.