The induction of immunologic unresponsiveness to improve renal allograft survival was attempted in 163 patients by the pretransplant administration of donor-specific whole blood or buffy coat in conjunction with continuous Aza immunosuppression. All donor-recipient combinations were at least one-haplotype disparate, and 21 were two-haplotype disparate. Transient sensitization occurred in 2% and permanent sensitization in 7%. Over a 10-year period, the DST+Aza allograft survival rate is similar to the HLA-identical sibling transplants. The CMV sepsis rate was only 2%, and there were no lymphoproliferative neoplasms. The low rate of sensitization (7%) has permitted almost all patients to undergo eventual renal transplantation from the specific blood donor. This and the low rate of early rejection (3%) argues for a modification of the immunologic response.