A series of 200 cases of full-thickness corneal allografts have been followed to determine whether HLA and ABO incompatibility influence prognosis of the grafts. 85% of patients with avascular corneas had clear, functioning grafts one year after transplantation. Only 33% of patients with severely vascularised corneas had successful grafts one year after transplantation. A significant association was found between severe vascularisation of the patient's cornea and irreversible graft rejection. In this group of patients, the proportion of grafts functioning was found to be ranked according to the number of HLA antigens shared by graft donor and recipient. Patients receiving grafts matching for 2 HLA antigens showed a failure-rate due to irreversible rejection of 26% at one year, in comparison with 57% and 62% of grafts matching for 1 or 0 HLA antigens respectively. ABO incompatibility or ABO phenotype of the recipient did not influence graft prognosis. The results indicate that patients with severely vascularised corneas should receive HLA-matched corneal grafts. The institution of HLA-typed cornea "banks" for treatment of such patients is advocated.