We report a retrospective series of 156 penetrating keratoplasties that were performed in 144 patients during a two-year period, with a minimum of one-year follow-up. Three different types of rejection were identified--endothelial rejection, epithelial rejection, and subepithelial infiltrates (SEIs). We also report the clinical signs, frequency, preoperative correlates, significance, and treatment of each type of rejection. The overall frequency of any kind of rejection was 29%. Endothelial rejection was seen in 21% of the grafts, epithelial rejection was seen in 10% of the grafts, and SEIs was seen in 15% of the grafts. The frequency of endothelial rejection increased with preoperative corneal vascularization. All three types of rejection decreased in frequency with the increasing age of the recipient. Endothelial rejection was more successfully treated in the cases that had no preoperative stromal vascularization.