Cell-mediated cytotoxicity against syngeneic MC104 fibrosarcoma cells was detected in C57BL/6N mice 7 days after tumor inoculation in the hind foot. This cytotoxicity was undetectable by Day 14 in the Winn test using spleen and draining popliteal lymph node (DPLN) cells. Similar results were obtained with the 51Cr release assay following in vitro activation of these lymphoid cells with mitomycin C-treated tumor cells. The antitumor cytotoxicity was shown to be mediated by T-cells. Spleen but not DPLN cells from 14-day tumor bearers enhanced tumor growth in the Winn test, suggesting the presence of immunosuppressor cells in the spleen. Two intralesional injections of 50 microgram of cell wall skeleton (CWS) of Nocardia rubra on Days 2 and 7 resulted in apparent tumor growth inhibition and prolongation of the survival period of tumor bearers. DPLN cells from tumor bearers treated with N. rubra CWS exhibited significant recovery in the cytotoxicity tested on Day 14, whereas the recovery in that of spleen cells was not apparent. The cytotoxicity augmented by N. rubra CWS was specific to MC104 tumor cells and was shown to be mediated by T-cells. These cytotoxic T-cells were shown to be able to localize not only in DPLN but also in the spleen and tumor in mice receiving the intralesional immunotherapy with N. rubra CWS. These results suggest that T-cell-mediated cytotoxicity against syngeneic tumor can be augmented by N. rubra CWS and might play an important role in the systemic development of its antitumor effect, although the effector cell increase in the spleen might be suppressed by splenic suppressor cells during tumor growth.