In an analysis of 4851 first cadaver kidney transplants, a statistically highly significant correlation was found between the number of HLA antigens mismatched and graft survival (P < 0.0005 at 1 yr). The difference in the survival rates of grafts with no HLA mismatch compared with grafts with 4 mismatches was 11-12%, similar to results of previous analyses. HLA-A locus antigens had a slightly stronger effect than B locus antigens. The correlation of HLA matching with graft survival was most significant at centers with poor overall transplant outcome, and there was no correlation at centers with very good overall results. Presensitization also had the strongest effect at centers with poor overall graft survival.