Dermal ulcers related to infiltration of advanced cancer often release destruction-associated effluvia (cancerous malodor). We encountered a patient in whom metronidazole (MTZ) was effective for cancerous malodor at the dermal ulcer site related to pleural metastasis, involving the thoracic wall, from gastric cancer. The patient was a male in his 60's. As left subphrenic abscess associated with suture failure at the anastomotic site after surgery for gastric cancer led to pyothorax via the transdiaphragmatic route, a thoracic drain was inserted. Furthermore, bilateral pulmonary metastases and pleural dissemination were detected. Subsequently, the metastatic pleural focus infiltrated the thoracic wall via the space between the thoracic drain and chest wall. Its destruction resulted in fetid ulcer formation. The application of MTZ ointment relieved cancerous malodor. In addition to assessment using an odorimeter, the patient's subjective evaluation-based score confirmed the efficacy of this agent. Palliat Care Res 2009; 4(2): 339-345