1. Pretransplant blood transfusions improved the survival of first cadaver donor renal allografts by 10% at one year in CsA-treated recipients. 2. Pretransplant transfusions improved the survival of living-related donor transplants as well. HLA-identical sibling grafts had a 5% higher graft survival rate in transfused than nontransfused patients. Living-related donor transplants in one haplotype-mismatched combinations had a 10% higher one-year graft survival rate in transfused recipients. One-year graft survival in nontransfused recipients of one haplotype-mismatched sibling transplants was 75%, a result slightly lower than that for CsA-treated first cadaver donor recipients. 3. Transfusions given prior to retransplantation did not improve survival of the second graft. As patients who have previously rejected a transplant are at high risk of sensitization, blood transfusions should be avoided if possible. 4. For black recipients, transfusions improved one-year cadaver graft outcome by 17%. The effect was smaller in white recipients (8%), but significant nevertheless. One-year graft survival was 55% in nontransfused blacks and 68% in nontransfused whites. The impact of recipient race on the transfusion effect may explain some of the discrepancies between the UCLA and European registries on the magnitude of the transfusion effect. 5. Even centers with high overall success rates with cadaver donor transplants had poor graft survival in nontransfused recipients. The transfusion effect cannot be explained simply as a reflection of center performance. 6. The number of transfusions required to see an improvement in graft survival was small. Even a single transfusion significantly improved graft outcome in male and nulliparous female recipients. Since the risk of sensitization increased with multiple transfusions, large numbers of unnecessary transfusions should be avoided. 7. There may be alternatives to transfusion for those patients unwilling or unable to accept blood products and for patients at high risk of sensitization (parous females) as a result of transfusion. HLA matching resulted in high survival rates among nontransfused recipients.