Sequence-specific oligonucleotide probe hybridization and sequence-specific primer polymerase chain reaction (PCR) typing suggested the presence of variants of HLA-B*40 in three individuals. Two were part of 3,500 potential marrow donors being screened for the National Marrow Donor Program, while the third was a clinical specimen. PCR products encompassing HLA-B locus exons 1 through 3 were prepared and subcloned. In one individual, a native of the Pacific Islands, sequencing revealed a novel HLA-B*40 allele (B*4023). In two other individuals, a previously unknown exon 1 sequence was determined for HLA-B*4016 (ethnicity unknown) and B*4020 (Hispanic). These findings further illustrate the substantial genetic variation present at the HLA-B locus within human populations.