Five patients with end-stage renal disease received bone marrow and kidney transplants from HLA-mismatched living related donors. Transient hematopoietic chimerism developed in all five. In one patient, irreversible humoral rejection occurred. In the other four recipients, immunosuppressive therapy was discontinued after 9 to 14 months and renal function has subsequently remained stable. Five patients with end-stage renal disease received bone marrow and kidney transplants from HLA-mismatched living related donors. In four recipients, immunosuppressive therapy was discontinued after 9 to 14 months and renal function has subsequently remained stable. Long-term results of organ transplantation remain unsatisfactory, mainly because of chronic rejection and complications associated with immunosuppressive medications. 1 , 2 Immune tolerance, which has been achieved in animal models, might provide a means for avoiding both of these problems. However, the results of attempts to extend such studies from laboratory animals to humans have been disappointing. 3 – 7 Tolerance of allografts has been induced in mice 8 and larger animals 9 by first transplanting hematopoietic stem cells from the prospective donor into the recipient, thereby creating a lymphohematopoietic chimera in which donor and recipient hematopoiesis coexist (“mixed chimera”). Using a nonmyeloablative perioperative regimen, we . . .