AbstractA polyclonal CD34‐8‐WT31‐cell line (termed SFG) was utilized for mice immunization in order to produce monoclonal antibodies (mAb) specific for the T cell receptor (TcR) γ/δ. Hybrid supernatants were screened for their ability to induce SFG cells (but not conventional TcR α/β CTL lines) to kill the murine Fc receptor‐positive P815 target cell line. Three hybrids, termed G1, A13 and F11, were isolated according to this screening. By indirect immunofluorescence G1 mAb reacted with 65% of SFG cells, while A13 stained 26% and F11 75% of cells. Double‐fluorescence analysis revealed that G1 and A13 mAb identify two distinct, non‐overlapping subsets of cells present in the SFG cell line. The reactivity of the mAb was also analyzed on a panel of representative TcR α/β clones. G1 mAb reacted with 5 clones, that were also stained by the previously described BB3 mAb (recognizing the disulfide‐linked form of TcRα/β). These clones failed to react with A13 and δ‐TCS‐1 mAb (the latter of which is known to react with a non‐disulfide‐linked form of TcR α/β). Out of six clones that reacted with A13 mAb, four were also δ‐TCS‐1, whereas two were δ‐TCS‐1‐and none of them reacted with G1, (or BB3) mAb. In contrast to the mAb above, F11 brightly stained the G1A13‐clones and more weakly the G1‐A13 clones. Moreover, F11 efficiently triggered both types of clones to kill the P815 target cells while G1 and A13 were able to trigger only G1 or A13 clones, respectively. None of the mAb above reacted with a large number of CD3WT31 clones. Antibodyinduced surface antigen modulation experiments indicated that molecules recognized by G1, A13 and F11 were physically associated on cell surface with CD3 determinants. In addition, immunoprecipitation followed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis analysis (performed on125I‐surface‐labeled TcRα/β clones) revealed that molecules recognized by G1, A13 and F11 displayed an apparent mol. wt. corresponding to that of CD3‐associated TcR molecule