A novel human leukocyte antigen-B (HLA-B) allele, B*420502, was identified in a patient with leukemia (Caucasoid, Czech ancestry) and his mother during intrafamily search for the hematopoietic stem cell donor. The novel allele was initially detected by HLA typing at low resolution using both sequence specific primers and sequence specific oligonucleotides techniques that resulted in unique reaction patterns. The alleles of the HLA-B locus were separated by the haplotype-specific extraction technique. Sequencing of those alleles revealed a novel allele, B*420502, that is identical with B*420501 except a T-->G exchange (synonymous mutation) at position 618.