The exon 2 nucleotide sequences of HLA-DQwl-associated and DQw3-associated HLA-DR"Br" alleles were determined from genomic DNA amplified by the Taq polymerase chain reaction technique. Both alleles reveal identical exon 2 nucleotide sequences. Comparison with other DR alleles suggests that DR"Br" may have originated from DR1 by gene conversion with DR4-Dw10, DR5, or DRw6-Dw18 third hypervariable region sequences.