An extensive family study on HLA-DPB1 was performed in 105 families living in northeastern Japan. In a linkage study between HLA-DPB1 and other HLA loci, five apparent recombinations between DPB1 and DR/DQ loci were observed. The recombination frequency (theta) with maximum probability was estimated to be 0.017 by the lod score method. DPB1 allele and haplotype frequencies in unrelated parents were determined by direct counting. The most common allele was DPB1*0501 with the frequency of 41.2% and the second was DPB1*0201 with 24.0%. Nine DPB1-DR and six DPB1-DQ haplotypes were in significant linkage disequilibrium. Seven kinds of extended haplotypes were observed to be over 1%, in which the most common haplotype A24-B52-DR15-DQ6-DPB1*0901 occurred at 6.0%. Moreover, we found two "new" DPB1 alleles in this study. The first one possesses a single base substitution from DPB1*0501 resulting in an amino acid change. The other is most likely to be formed by an intraexonic recombination between DPB1*0301 and DPB1*0501.