1. In an unselected adult renal transplant population, FK506 as the primary immunosuppressive agent yielded one- and 2-year actuarial patient survival rates of 95% and 93% and one- and 2-year actuarial graft survival rates of 89% and 83%, respectively. Forty-nine percent of successfully transplanted patients were weaned off steroids. 2. In pediatric renal transplant patients, FK506 has been associated with 100% one- and 3-year actuarial patient survival rates and 98% and 85% one- and 3-year actuarial graft survival rates, respectively. Sixty-two percent of successfully transplanted patients were taken off prednisone, with dramatic improvements in height. 3. FK506 has been used successfully in rescuing 70-74% of adult or pediatric renal transplant patients with an acute rejection that failed conventional therapy. 4. Kidney/bone marrow transplantation under FK506 therapy has been successfully performed without graft-versus-host disease and with routine augmentation of chimerism. 5. The side effects of FK506 included nephrotoxicity, neurotoxicity, and diabetogenicity; they were comparable to those seen with CsA. 6. FK506 is an important new addition to the immunosuppressive armamentarium in renal transplant patients.