The TCR in a mature T cell is a multimeric complex of TCR α and β chains, and CD3 subunits. Functional TCR α and β chains are encoded by genes that result from developmentally controlled somatic rearrangement events. By FACS analysis, we have detected a TCR Vβ8 protein on the surface of an immature lymphoid cell line, C1-V13D, that has all of its TCR genes in germline(unrearranged) configuration. RNA blot analysis detected a 1.4 kb polydenylated Vβ8 RNA in C1-V13D cells, but no expression of Cβ was detected. Rapid amplification of 3' cDNA ends was used to clone an RNA that was initiated from the leader exon of the Vβ5.1 gene and spliced to the V exon of the Vβ8.2 gene. The putative sequence of the mature 10.8 kDa protein was entirely encoded by the Vβ8.2 exon. RT-PCR analysis confirmed that 97% of the Vβ8 RNA detected in C1-V13D cells was encoded by the Vβ8.2 gene, and only 3% by Vβ8.1 and Vβ8.3 genes. Furthermore, most of the Vβ8.2 RNA was spliced to the leader exon of the Vβ5.1 gene and not to the leader exon of the Vβ8.2gene. The implications of preferential transcription from particular germline TCR genes for repertoire diversity and possible functions for proteins translated from germline TCR Vβ genes are discussed.