Forty-eight patients with corneal grafts with severe endothelial rejection were randomly assigned to two treatment groups. One group of 24 patients received prednisolone acetate 1% drops hourly and a single intravenous pulse of 500 mg methylprednisolone. The other group of 24 patients received the same topical therapy plus oral prednisone 60 to 80 mg daily. Nineteen (79.2%) grafts survived in the group that received pulse therapy compared with 15 (62.5%) grafts in the oral group; the difference was not significant (P = 0.17). However, in patients who sought treatment early (less than or equal to 8 days) survival rates were 92.3% and 54.5%, respectively, which indicated a significant advantage for pulse therapy (P less than 0.05). Pulse therapy also appeared beneficial in preventing subsequent rejection episodes. Five (26.3%) of the 19 surviving grafts in the group that received pulse therapy had a further rejection episode compared with 10 (66.7%) of the surviving 15 grafts in the oral group; the difference is significant (P less than 0.025).