The influence of the RL‐A (RabbitLeukocyte — locusA) histocompatibility system upon the corneal immune response to interlamellar allotransplantation was studied in 75 rabbits. The evaluation of histocompatibility was based upon reactions with 18 different lymphocytotoxic rabbit isoantisera obtained by pairwise immunization of outbred rabbits. These sera were tested against pure lymphocyte suspensions from the potential corneal donors and recipients.The evaluation of the immune reaction was performed by clinical observation, by photographs, and histologically in sections of the eyes and in conjunctival scrapings.The immune reaction to allotransplantation was weak and consisted of lymphocyte infiltration around the graft. Immune reaction was seen only in histoincompatible transplantations, compatible ones showed no reaction. The lymphocyte infiltrations were more pronounced when the noncompatible animals were presensitized by donor skin grafts. In contrast to this no reaction could be produced in compatible animals presensitized by donor skin grafts. Histocompatibility evaluation may be of clinical importance in corneal transplantations if the recipients have been presensitized to histocompatibility antigens by previous transplantations, transfusions, or pregnancies, especially if the recipient cornea is vasculari