A 435-kilobase (kb) DNA segment, which is centromeric to HLA-B in the human major histocompatibility complex, was isolated by chromosome walking with overlapping cosmids. Within the cloned region, the genes for the tumor necrosis factors (TNFs) alpha and beta and HLA-B were 210 kb apart. The human homolog of a mouse gene, B144, was located next to TNF alpha. Moreover, the presence of additional genes was suggested by a large cluster of CpG islands. With cosmid probes, several distinct transcripts were detected in RNA samples from a variety of cell lines. Altogether, five novel genes were identified by isolation of corresponding complementary DNA clones. These "HLA-B-associated transcripts" (BATs) were mapped to different locations within a 160-kb region that includes the genes for TNF alpha and TNF beta. The presence of the genes for BAT1 and BAT5 in the vicinity of HLA-B again raises the question of which gene in this region determines susceptibility to ankylosing spondylitis.