The T cell receptor (TcR) beta chain is encoded by a 1.3-kb mRNA which contains variable (V), diversity (D), joining (J) and constant (C) regions. A shorter 1.0-kb transcript with C but no V sequences is found in thymocytes, alpha/beta and gamma/delta T lymphocytes and natural killer cells. The origin, clonal variability and function of this transcript is unknown. We isolated cDNA clones representative of the 1.0-kb mRNA from cDNA libraries of either polyclonal or clonal natural killer and gamma/delta lymphocytes. Ten different types of cDNA clones belonging to three separate groups were identified: (a) "J-C clones" consisting of one of five J beta regions and the corresponding C beta 1 or C beta 2 regions; (b) "D-J-C clones" composed of D beta 1/or D beta 2/J beta rearranged sequences and C beta 1 or C beta 2 sequences; (c) "5'C clones" made up of C beta 1 or C beta 2 regions preceded by the corresponding genomic 5' flanking region. The presence of recombination signal sequences in J-C and D-J-C clones suggests that the first derive from mRNA transcribed from promoters located in the 5' J region and the second from mRNA transcribed from promoters situated in the 5' D region. Nucleotide sequence analysis demonstrated that only three of the ten types of clones isolated had the potential to code a short cytoplasmic T beta protein with a variable D-J beta N terminus. These findings have implications for the mechanisms of T beta germ-line transcription and the function of the T beta transcripts.