Twenty-four patients with corneal homografts were repeatedly evaluated by the leucocyte migration test using pooled human corneal extract 0.2 mg/ml as antigen. All patients were treated with small doses of local or systemic steroids. If cloudiness of the graft developed, the doses were increased up to 40 mg methylprednisolone or 48 mg triamcinolone daily. Before transplantation, two patients showed inhibition of leucocyte migration. During the third postoperative week seventeen responded with migration inhibition. The grafts remained clear in all but one patient during this period of time. After the second postoperative month, leucocyte migration inhibition was found in none of sixteen patients whose grafts remained clear. Three of seven patients with late graft rejection exhibited migration inhibition and in two of them this response was demonstrated repeatedly several months prior to the clinical reaction. These findings suggest that the test may predict graft failure in some patients.