The search for the genes encoding the T-cell receptor α and β chains revealed a third gene, Tγ (ref. 1), which shares with the Tα (refs 2-7) and Tβ (refs 8-15) genes a number of structural features, including somatic rearrangement during T-cell development. Tγ gene expression appears to be unnecessary in some mature T cells16,17 and is at its greatest in fetal thymocytes18,19, encouraging speculation that Tγ has a role in T-cell development and may be involved in the recognition of polymorphic major histocompatibility complex (MHC) products during thymic education20,21. One argument against the participation of Tγ in such a process has been its apparently limited diversity, due to the small number of gene segments available for rearrangement1,22. We here describe the identification of additional Tγ V-gene segments and demonstrate that they can be rearranged to previously identified J- and C-gene segments and are expressed in fetal thymocytes. In addition we describe a variety of patterns of Tγ mRNA processing which may be significant for Tγ gene regulation.