Diffuse panbronchiolitis (DPB) is an unusual form of bronchiolar disease affecting exclusively East Asians. Strong associations of DPB with the class I human leukocyte antigens HLA-B54 in Japan and China and HLA-A11 in Korea suggest that the susceptible locus for DPB is located between the HLA-B and HLA-A genes. We have previously reported that the susceptibility gene for DPB could be localized within a 200-kb segment between the S and TFIIH loci in the HLA class I region, using refined microsatellite-based association mapping. However, no genes have been recognized in this candidate region to date. In order to identify a novel candidate gene for DPB from this segment, the expressed sequence tag databases were searched using the genomic sequence. As a result, a cDNA clone was isolated from a human lung cDNA library. This gene, designated C6orf37 (Chromosome 6 open reading frame 37), spans approximately 2.5 kb and consists of two exons encoding a 235-amino acid protein, sharing homology with the mucin-like domain of human zonadhesin, which is a sperm multiple-domain transmembrane protein with the sperm zona pellucida binding activity. Unexpectedly, RT-PCR analysis detected transcripts from the anti-sense DNA strand of this C6orf37 locus. The gene designated as C6orf37OS (C6orf37 Opposite Strand) and represented by these anti-sense transcripts contained no open reading frame. The transcripts from C6orf37 and C6orf37OS were observed in numerous tissues, with most-abundant expression in lung, kidney, and testis. Taken together, these results, especially the abundant expression in lung, indicate that C6orf37 and C6orf37OS are excellent candidate genes for DPB.