HLA-DP antigens have many biological features in common with products of the HLA-DR and-DQ subregions. They have been shown to function as restriction elements in antigen presentation. A few associations between DP alleles and diseases have been described. HLA-DP antigens have also been indicated to act as transplantation antigens. Until recently, HLA-DP polymorphism has been investigated by the primed lymphocyte typing technique (PLT). However, the PLT assay is difficult to standardize and in most series a gene frequency of untypeable individuals of 1045% is obtained. Furthermore, the PLT method most probably does not detect all the biologically relevant polymorphism indicated by biochemical studies, restriction fragment length polymorphisms (RFLP) and by sequencing of the polymorphic second exon of HLA-DPAZ and-DPBI genes. DP typing by RFLP analysis and the correlations between specific RFLPs and the PLT-defined DP specificities have been most thoroughly investigated by Hyldig-Nielsen et al.(1). By MspI DPA and DPB RFLP typing, all the recognized cellularly-defined DP specificities (DPw l-DPw6) can be distinguished except D h 3 and DPw6 (1, 2). However, DPw6 is a very rare allele in Caucasians. In addition, the local specificity CDP-HE1 can be identified (3).