We report two cases of pleomorphic carcinoma with fever and severe inflammatory reaction. In case 1, an abnormal mass shadow was found on the chest X-ray film of a 63-year-old man with bloody sputum. After right upper lobectomy, the tumor was diagnosed as pleomorphic carcinoma. About 7 months after surgical operation, he had fever and chest pain. Although his test results showed leukocytosis and his elevated serum CRP level indicated some infection, there were no signs of bacterial or fungal infection. Further examination revealed metases of lung cancer in the left adrenal gland, mediastinal and iliac lymph nodes. Serological study revealed elevated level of G-CSF, likely due to G-CSF producing metastatic tumors. In case 2, a 77-year-old man presented with continuous high fever. Examinations revealed elevated serum CRP level and multiple nodular shadows and enlarged supraclavicular and mediastinal lymph nodes on the chest CT, suggesting some infectious, connective tissue, or lymphoproliferative diseases. He was finally found to have pleomorphic carcinoma of the lung by histological examination of lymph nodes. The continuous high fever seemed to be a tumor-related fever, because it rapidly disappeared after administration of naproxen.