For most HLA-B alleles, coding sequences of the 3 0 part of the genes still need to be determined, and sequences of the 3 0 noncoding regions have yet to be studied systematically. In this study, we have determined the sequences of introns 4-6 in all HLA-B allelic groups, and computed nucleotide substitution rates and phylogenetic relationships. These sequences demonstrated an inconsistent pattern of intralineage specificity, intralineage diversity, and interlineage diversity that is best characterized by a patchwork pattern. Apart from phylogenetic studies about HLA diversity and diversification, the sequence data obtained in our study may prove valuable for haplotype-specific sequencing of the 3 0 part of HLA-B and for the explanation of recombination events in newly described HLA-B alleles.