A patient with complaints of high fever and left shoulder pain was found to have a large mass in the left upper lobe on chest roentgenogram. Laboratory evaluation revealed marked thrombocytosis, hypoalbuminemia, and increased serum concentrations of CRP, fibrinogen and interleukin-6 (IL-6). A transcutaneous biopsy specimen revealed large cell carcinoma. Tumor production of IL-6 was confirmed by immunohistochemical staining with an anti-human IL-6 monoclonal antibody (MH60).