Various factors affect the outcome of renal transplants in humans. Matching for HLA-A, -B, and -DR histocompatibility antigens improves survival rates for renal allografts from first cadaver donors. Zero-HLA-A- and -B-antigen-mismatched grafts and two-HLA-DR-antigen-matched grafts do better, although results differ depending on the recipient's primary renal disease. Pretransplant third-party blood transfusions significantly improve survival rates of cadaver donor allografts. The mechanism of this beneficial effect has not been identified; however, blood transfusions probably do not "select out" high responders among potential recipients by stimulating the production of lymphocytotoxic antibodies. Cyclosporine has been heralded as a potent, nonspecific immunosuppressive agent that will significantly improve renal allograft survival rates. The selectivity of cyclosporine's effect on T lymphocytes is advantageous; however, its side effects, especially nephrotoxicity, may limit its usefulness. Attention to the potential surgical complications of renal transplantation can significantly reduce morbidity and mortality.