Allelic sequence variation of the HLA DP-alpha and DP-beta genes has been analyzed in a panel of 34 DP-typed cell lines. The polymorphic second exon of these genes was specifically amplified in vitro by the polymerase chain reaction method, using the thermostable DNA polymerase of Thermus, aquaticus. The analysis of M13 clones containing the amplified DP-beta sequences revealed a total of 14 allelic variants. In general, specific allelic DP-beta sequences were associated with each of the defined DPw1-w6 types, with beta allele subtypes revealed for the DPw2 and DPw4 specificities. An additional six DP-beta alleles which did not correlate with any of the T cell-defined specificities (DP "blanks") were also identified. Only the two previously characterized alleles of DP-alpha were detected. These observations suggest that the T cell-defined DP specificities are determined by polymorphic residues on the beta-chain. The sequence polymorphisms in DP-beta are clustered in a few specific regions, and can be detected using sequence-specific oligonucleotide probes and polymerase chain reaction amplified DNA in a rapid dot-blot format. This approach provides a simple and informative method of DP typing. The DP-beta sequences derived from four DP-typed celiac disease patients were compared with the distribution of DP-beta alleles in control individuals.