Penetrating keratoplasty is the most common form of solid organ transplantation.Owing to recent developments in surgical techniques, materials and postoperativemanagement, indications for PK have been extended to high risk patients.Corneal grafting is a successful procedure with a first year survival rate of up to90%, however a long-term 10 year survival rate drops to 62% and in ‘high risk’eyes can be as low as 35%. The most common cause of corneal graft failure isallograft rejection and endothelial damage accounts for most of the morbidity.Despite the anterior eye chamber immune privilege, graft rejection is a majorcomplication of penetrating keratoplasty as they facilitate subsequent graft failure.Acute rejection which may occur weeks to years after transplantation involves bothhumoral and cell-mediated immune reactions. The pathogenesis of chronicrejection is not clear.