The physiological role of lymphocytes bearing the gamma delta T-cell receptor (TCR) is still unclear. A function for a subset of these cells, however, is inferred from the finding that certain gamma delta chain-bearing lymphocytes are stimulated in a receptor-dependent fashion by mycobacterial antigens. We found that hybridomas derived from such cells in newborn murine thymus not only responded to mycobacterial purified protein derivative (PPD), but also exhibited an apparent autoreactivity. In neither response was haplotype-specific major histocompatibility (MHC) restriction demonstrable. To investigate the nature of antigen recognition by these gamma delta+ cells, we sequenced the gamma- and delta-chains from 28 PPD-reactive hybridomas, and found that a specific gamma-chain, together with one of a limited set of delta-chains, was needed to generate the PPD specificity. The reactive gamma delta pairs exhibited considerable junctional diversity, which may act to produce differences in the fine specificities of the responding cells.