gamma delta T cells bearing the V gamma 9 gene segment have been shown to recognize staphylococcal enterotoxin A (SEA) and a range of other Ags including mycobacterial Ags. We have established an experimental system to analyze the recognition properties of human TCR-gamma delta on a molecular level by transferring the receptor from its original T cell into a Jurkat T cell host that does not express an endogenous TCR. Three groups of transfectants that express the same delta-chain, V delta 1, but different gamma-chains (V gamma 9-J2-C gamma 2, V gamma 3-J2-C gamma 2, and V gamma 9-JP-C gamma 1) together with the endogenous CD3 were obtained. The transfectant T cells each expressing different gamma delta receptors all produced IL-2 after stimulation with plastic bound anti-CD3 Ab, but only those expressing V gamma 9 responded to stimulation with SEA in the presence of an autologous lymphoblastoid B cell line. In addition, transfectants that expressed V delta 2 combined with V gamma 9 could also respond to SEA. These results indicate that the V gamma 9 portion of the receptor, independent of the J region and C region or the delta-chain, is responsible for recognizing SEA.