A better than 70% 1-year graft success rate was obtained in highly sensitized recipients of first and second kidney transplants. Recipients of third or fourth transplants had a 25% lower success rate. 2. The results of this trial show a strong influence of HLA matching in highly sensitized recipients. HLA-DR mismatches appear to be most deleterious, followed by HLA-B mismatches. 3. Thirty transplants with 0 mismatches for HLA-B, -DR had an excellent 88% 1-year graft survival rate. 4. The strong effect of HLA matching mandates the national and international exchange of kidneys for highly sensitized recipients.