In contrast to organ transplantations corneal grafts are tissue transplantations with the advantage of a minority of immune stimulating cells. The incidence of allograft rejections is greater in penetrating grafts than in lamellar grafts because of endothelial immune reactions. The decompensation of the graft is caused by the damage of the endothelial layer. The influence of HLA-A, -B and -DR matching is proven in case of vascularised cornea or of repeated perforating keratoplasty. The introduction of the immunosuppressive therapy with Ciclosporin A was successful in maintaining a clear graft.