Using allogeneic T-cell recognition we have previously defined five new histocompatibility antigens designated "SB" antigens. To standardize typing for these antigens, cryopreserved, primed lymphocytes are now used as standard reagents and a technique of cluster analysis has been modified to score typing results objectively. Two primed lymphocyte reagents are used to define each SB antigen; although derived from independent responder-stimulator combinations, the concordance between the reagents is good (r is greater than 0.86). The SB-antigen distribution in a population of 215 normal donors in consistent with Hardy-Weinberg equilibrium of alleles of a single locus. Estimated gene frequencies ranged between 3 percent (SB5) and 36 percent (SB4) with 31 percent blanks. Analysis of association between the SB antigens and A, B, DR antigens in 200 normal donors revealed that associations were generally weak with a few exceptions, in particular, the A1, B8, DR3, SB1 "haplotype" and also the B7, DR2, SB5 "haplotype".