The Collaborative Cornea Transplant Studies (CCTS) comprised two randomized, double-masked, clinical trials, the Antigen Matching Study (AMS) and the Crossmatch Study (CS), designed to determine whether matching HLA-A, -B, and/or HLA-DR antigens, donor-recipient crossmatching, or ABO compatibility reduced the risk of corneal allograft rejection and failure in high-risk patients. The studies showed that for patients needing a corneal graft with uncompromised immune systems and at high risk for corneal graft rejection: (1) neither HLA-A, -B, nor HLA-DR antigen matching substantially reduces the likelihood of corneal graft failure; (2) a positive donor-recipient crossmatch does not dramatically increase the risk of corneal graft failure; and (3) ABO blood group matching may be effective in reducing the risk of graft failure. Intensive steroid therapy after transplantation, frequent follow-up, medication and follow-up compliance, and patient education appear to play a significant role in corneal graft success.