The application of the polymerase chain reaction (PCR) technique permits the rapid matching between individuals of HLA-DR-Dw specificities. The technique exploits the formation of mismatched DNA hybrids (heteroduplexes) which are formed at the end of each PCR cycle between coamplified products of the second exons of expressed DRB genes and DRB pseudogenes. Although PCR fingerprinting is a simple and effective technique for HLA-DR-Dw matching, extension of the heteroduplex principle to HLA-DP matching is not directly possible because for DPB1-specific PCR primers, generally only a single PCR product exists. It is possible, however, to generate PCR fingerprints for the DPBl locus by spiking reactions with a specialized molecular construct which the authors have termed a universal heteroduplex generator. The initial development of DNA heteroduplex matching was in response to an urgent clinical need for a fast screening method for selection of DR-Dw and DP matched unrelated donors for patients awaiting bone marrow transplantation.