The relationship between transfusion of different preparations of blood, sensitization to HLA antigens and survival of subsequent kidney transplants was investigated in 90 consecutive recipients. HLA lymphocytotoxins in transplant candidates precluded or greatly delayed receipt of an allograft (p less than 0.0005). Furthermore, only 17% of such sensitized recipients had functioning grafts one year after transplantation compared to 57% survival for nonsensitized recipients (p less than .02). A small number of nonsensitized patients who were never transfused had surprisingly poor one year graft survival (25%). If frozen blood is used for transfusion rather than whole/packed RBC, the incidence of patient sensitization can be markedly reduced without subsequent compromise in transplant survival (51%). It is concluded that as a consequence of avoiding HLA sensitization by transfusion of frozen blood (processed by agglomeration), the period of hemodialysis required for potential graft recipients will be shortened and an increased proportion of potential recipients will be successfully treated by transplantation.