A 38-year-old man was admitted with persistent productive cough and right anterior chest pain. Chest X-ray showed two large masses connected with each other, one in the right lung field and the other in the anterior mediastinum. A tentative diagnosis of either lung abscess or bronchogenic carcinoma was initially made, because of elevated serum tumor markers (SLX and SCC) and persisting refractory inflammatory sings. However, open chest drainage revealed a few fine hairs and atheromatous materials within the masses, and the diagnosis of teratoma was made. We removed these masses, and investigated the reason for the elevation of tumor markers. Staining with SLX monoclonal antibody demonstrated that the pancreatic tissue in the masses contained SLX. Although this is the first reported case of teratoma producing tumor marker (SLX), it is highly possible that tumor markers may be elevated in the majority of patients with teratoma because of the genesis of this tumor.