Human eye bank corneas were preserved in M-K medium for varying periods of time after which viability of the endothelial cells was evaluated by vital staining and scanning and transmission electron microscopy. Endothelial viability and ultrastructural integrity was maintained in some corneas up to four days. Twenty-five consecutive keratoplasties were performed utilizing human donor material stored in M-K medium. There were clear grafts in 92% of the cases and there were no primary graft failures. After the ninth postoperative week, the average central corneal thickness was 0.47 mm and 23 of the 25 grafts remained clear to moderately clear. All of the donor material used for keratoplasty was stored in M-K medium for less than 80 hours.