This is a proposal to continue to evaluate the Heterophile Transplantation Antigen (HTA) in human transplantation. We propose to characterize and isolate HTA, determine its distribution in various tissues and at the cellular level. We will re-evaluate the immunopathology of human renal allograft rejection in an effort to separate pathology related to HLA and/or HTA. The ultimate goal is to prospectively type for HTA compatibility in renal transplant patients. We believe this will lead to better clinical management and better allograft survival.