1. The fraction of patients and graft survival was provided for amino acid residues, heptapeptides, and conformational epitopes with HLA specificities of up to 7 antigens mismatched. 2. Mismatching large numbers of serologically defined residues was detrimental to graft survival, whereas nonserologically defined residues did not have an effect. 3. The difference in graft survival for those with a few and those with many conventional A,B,DR mismatches was doubled by counting serologically defined peptide epitopes. 4. The attempt to create conformationally defined epitopes by taking adjacent variable residues did not provide a good correlation with graft outcome.