We have previously reported the complete sequence of the cDNAs corresponding to the alleles at the polymorphic loci (DRB1, DRB3, DQA1, DQB1) of the DRw11 (5) cell line Swei. We now report the nucleotide and derived amino acid sequence of the alleles at the remaining two polymorphic loci, DPA1 and DPB1, from Swei, which types as DPw4b. Comparison of the DPw4bα sequence with previous DPα sequences indicates that it is identical to the DPα chains of DPw4 and DPw2. However, the DPw4bα cDNA encodes a unique 3′ untranslated region that corresponds to sequences contained within the last intron of the DPα genomic gene. These results indicate that alternative splicing occurs within the Swei DPα RNA. Comparison of the DPw4bβ sequence with previously reported DPβ sequences indicates that the first domain is identical to the sequence of the DPβ chain derived from the Burkhardt (Burk) cell line, but that the second domain differs by two amino acids. In addition, a single amino acid difference from DPw2 at position 69 in the first domain of the DPw4bβ chain suggests that this residue is important in determining DP specificity. Furthermore, comparison with other DPβ DNA sequences suggests that variable regions occur at positions 8-11, 55-57, and 84-87.