This communication describes a newly isolated T-suppressor (Ts) cell clone, BVI/5, derived from a CBA/J mouse tolerized to low doses of bovine serum albumin (BSA). The cells are Thy-1.2+, Lyt-1.1-, Lyt-2.1+, and express endogenous derived I-Ak and I-Ek molecules. BVI/5 Ts cells show antigen-specific I-Ek-restricted proliferation in the presence of antigen-presenting spleen cells. This proliferation can be inhibited by anti-I-Ek but not by anti-I-Ak monoclonal antibodies. In vitro antigen-specific suppressive capacity has been measured in a primed lymph node cell proliferation assay, and the fine specificity of these suppressor functions has been studied. Broader cross-reactivity in the specificity of this effector function is found if compared to the specificity of antigen-induced proliferation. The data extend previous findings on the expression of I-A and I-E molecules on Ts cells and are discussed with respect to the role of those cells in tolerance induction.