In an attempt to produce epitope specific antisera which could distinguish two closely associated HLA-DQ beta-chain alleles, we immunized 20 rabbits with synthetic peptides representing sequences from the first domain of the HLA-DQw8 and -DQw7 beta-chain molecules, differing only by one amino acid in position 57. Several of the antisera in immunoblotting specifically recognized either the HLA-DQw7 or the HLA-DQw8 beta-chain allele as previously reported. The fine specificity of the antisera was tested in ELISA using synthetic peptides of varying length as solid phase antigen. Two out of the 20 antisera specifically recognized DQw7 beta peptides and two antisera bound only to DQw8 beta peptides from the region containing the amino acid in position 57. To analyze whether the antisera bound to native HLA-DQ beta-chain molecules, FACS analysis was carried out. Seven of the 20 antisera bound to intact EBV-transformed B-lymphocytes, and one antiserum bound preferentially to HLA-DQw8 positive cells.