As shown by previous studies, the sheep erythrocyte-binding T11 molecule is involved in T cell activation, as well as in mechanisms of specific allogeneic target cell lysis. In this study, we utilized two anti-T11 monoclonal antibodies (mAb) that inhibited the specific cytolytic activity of mixed lymphocyte culture (MLC)-activated T cells to analyze, at the clonal level, the involvement of T11 molecules in (a) antigen-specific vs. nonspecific mechanisms of target cell lysis, and (b) antigen-driven T cell proliferation and interleukin 2 (IL 2) production vs. IL 2-induced cell proliferation. In contrast to anti-T3 or anti-T8 mAb, antibodies to T11 molecules inhibited the cytolytic activity of MLC-derived allospecific clones in a uniform manner. In addition, anti-T11 antibodies inhibited the specific activity of cytotoxic T lymphocyte clones resistant to anti-T3 antibodies, even after antibody-induced modulation of T3 molecules (while anti-T3 mAb had no effect). Similarly, anti-T11 antibodies inhibited the alloantigen-induced proliferation and IL 2 release of alloreactive clones independent of their T4+ or T8+ phenotype. The inhibitory activity of anti-T11 antibodies appears to be confined to antigen-specific T cell functions since neither natural killer-like activity of cytotoxic T lymphocyte clones nor the IL 2-induced clonal proliferation was affected. Thus, our results indicate that T11 molecules are functionally involved in antigen recognition by T cell regardless of their function and T4/T8 phenotype. The possible mechanisms of anti-T11 antibody-mediated inhibition are discussed.