In order to select MLC incompatible one-haplotype related donor-recipient pairs that would achieve better graft survival and in an effort to alter the recipient immune response, 45 patients received three fresh blood transfuions from their prospective kidney donors. Recipient sensitization was evaluated by cross-match testing weekly sera obtained during and after the blood transfusions against donor T- and B-lymphocytes at 5 C (cold) and 37 C (warm). Thirteen (29%) of the 45 potential related recipients developed a positive warm T-cell cross-match or a persistent warm B-cell cross-match to their blood donor and related transplantation was not performed. Thirty-two (71%) patients had an appropriate negative cross-match to their blood donor. Thirty of these patients subsequently received kidneys from their blood donor. Ninety-seven per cent of the kidneys are functioning from one to 25 months with a single graft failure due to a patient discontinuing immunosuppressive medication. In addition to the excellent graft survival there was an unusually low incidence of rejection episodes in the recipients of kidneys from their blood donor so that the posttransplant course paralleled that of HLA-identical siblings. This approach may have future application with two-haplotype mismatched donor-recipient pairs, both related and unrelated.