A pigeon cytochrome c-specific and Ia molecule-restricted T-cell hybrid was used as an immunogen in order to obtain monoclonal anti-antigen receptor antibodies. Two antibodies were isolated that specifically bound to and inhibited interleukin (IL) 2 release from only the immunizing clone. Lectin-induced IL 2 release was not affected by these antibodies. Binding assays with purified and iodinated monoclonal antibody indicated that there were approximately equal to 25,000 binding sites on the T-cell hybrid. Immunoprecipitation and NaDodSO4/polyacrylamide gel electrophoresis of detergent lysates from surface-labeled hybrid cells revealed a heterodimeric structure composed of chains of apparent Mrs 45,000-50,000 and 40,000-44,000. The chains were linked by intermolecular disulfide bonds, and the difference in migration of the isolated chains under reducing and nonreducing conditions was consistent with the presence of intramolecular disulfide bonds. The molecule that has been identified is a candidate for the antigen-specific receptor on the immunizing T-cell clone.