Lymph nodes draining progressive tumors contain tumor-sensitized but not functional preeffector T lymphocytes. These cells can acquire antitumor reactivity after stimulation with tumor cells and interleukin-2 (IL-2). We demonstrated here that, in the absence of tumor cells, preeffector cells could be stimulated and expanded by sequential culture with anti-CD3 monoclonal antibody and IL-2. The adoptive transfer of such activated cells mediated immunologically specific reductions of established pulmonary metastases. The therapeutic effects could be enhanced by the administration of IL-2. This activation represents a secondary immune response because effector cells could be generated only from tumor-draining but not from normal or adjuvant-stimulated lymph nodes. Furthermore, treatment of advanced metastases with these cells resulted in prolongation of survival and cure of the disease. Thus, anti-CD3 may serve as a universal reagent for activating tumor-sensitized T lymphocytes for cancer therapy.