62-year old man who had small cell lung carcinoma (SCLC) with subacute sensory neuropathy had an antibody (IgM) recognizing the antigen on peripheral nerves. The antibody in the serum recognized cell surface antigen on small cell carcinoma cell lines and also reacted with peripheral nerves simultaneously, but not with central nervous system. Two months before admission, he felt difficulty in walking because of paresthesias in the extremities. He was found to have a tumor shadow in chest X-ray, and was diagnosed as SCLC by biopsy of right supraclavicular lymph node. Western blot analysis demonstrated that auto-antibody (IgM) in the serum recognizing the antigen on the neuronal axon with single band at 29 kD. Pathogenesis of carcinomatous neuropathy is still unexplained, but the findings presented here have given rise to the possibility that anti-SCLC antibody may cross-react with neuronal antigen, primarily resulting in neuronal disorder.