A novel T cell receptor (TCR) subunit termed TCR delta, associated with TCR gamma and CD3 polypeptides, was recently found on a subpopulation of human T lymphocytes. T cell-specific complementary DNA clones present in a human TCR gamma delta T cell complementary DNA library were obtained and characterized in order to identify candidate clones encoding TCR delta. One cross-hybridizing group of clones detected transcripts that are expressed in lymphocytes bearing TCR gamma delta but not in other T lymphocytes and are encoded by genes that are rearranged in TCR gamma delta lymphocytes but deleted in other T lymphocytes. Their sequences indicate homology to the variable, joining, and constant elements of other TCR and immunoglobulin genes. These characteristics, as well as the immunochemical data presented in a companion paper, are strong evidence that the complementary DNA clones encode TCR delta.