The purpose of this investigation was to demonstrate host immune responses occuring in the fluid of a metastasized submandibular lymph node as a result of tumor cell cytotoxicity induced by superoxide anion (O_2^-) generated from neutrophils, and also, whether bleomycin (BLM) ointment injection to the lymph node augments such tumoricidal activity. The fluid of a metastatic submandibular lymph node was used as material. The patient was a 60-year-old female with gingival squamous cell carcinoma of the lower jaw. Neutrophil O_2^- generation was measured in terms of cytochrome C reduction. O_2^- generation levels of neutrophils in the fluid of a metastasized lymph node of the patient were higher as compared to those of peripheral blood neutrophils. Neutrophil O_2^- generation levels were slightly elevated one week after BLM ointment injection into the metastasized lymph node as compared to those seen in the period of pretreatment. In the fluid specimens from this lymph node, we observed a rosette formation comprised of a large central tumor cell surrounded by 4 to 12 neutrophils. In experimental study, in vitro cytotoxicity of neutrophils against scc-25 was demonstrated, as was rosette formation of scc-25 cells and neutrophils. These results suggest that tumor cell cytotoxicity occurs in the fluid of a metastasized lymph node as one of the host defence mechanisms, and further that cytotoxic activity may be enhanced by BLM ointment injection.