Thirty-eight HLA-A and -B locus specificities, for which the amino acid sequence is known, were cut by computer into all possible peptides composed of two to seven amino acids. These peptides were compared among the different specificities, and those that were unique were identified. For example, there were 375 unique tripeptides when considering both the A and B locus. The 1-year kidney graft survival was determined for patients who were mismatched for each of the tripeptides. The peptides were ranked according to the associated graft survival, and the sum of the ranks was used as a mismatching score. The rank sum score produced promising results, for some degree of correlation was noted when tested against another set of patients transplanted without CyA, and a third set of those who received grafts from related donors. We conclude that matching for tripeptides of the HLA-A and -B locus is associated with graft outcome, and that this may be a more effective way of HLA matching for transplants, particularly since a higher fraction of patients fall into the high-survival category.