Human B blast specific target determinants, selectively identified on PWM stimulated purified B lymphoblasts by in vitro generated CTLs, have previously been studied in the population and showed association to and inclusion of HLA-DR geneproducts. This report indicates that B blast target determinants are products of genes which in a codominant mendelain way segregate with the HLA haplotypes in 4 selected families. Furthermore tests of families with HLA-B/D, DR and HLA-D, DR/GLO recombinations show that human B blast specific target determinants are coded from loci (locus) in the HLA-D region, between HLA-B and GLO.