We have isolated and sequenced five germline V beta gene segments that are homologous to the V region of the YT35 cDNA encoding the beta chain of the T cell antigen receptor from the tumor MOLT-3. One of these gene segments is identical to the YT35 V segment, and therefore is the corresponding germline V beta gene segment encoding the YT35 cDNA. The other four V beta members exhibit 77-98% homology to the YT35 V gene segment. Two of these V beta gene segments are pseudogenes. Analyses of the coding region sequences reveal that, although the V beta segments are very diverse, they are mutating at a rate comparable to that observed in most eukaryotic genes. Analyses of the genomic clones show that the spacing distance between germline V beta gene segments ranges from 3 kb to greater than 30 kb, and the entire V beta 8 subfamily appears to be linked by a total of no more than 110 kb of DNA.