Paraneoplastic syndromes such as the subacute sensory neuronopathy (SSN) and paraneoplastic cerebellar degeneration (PCD) are associated with autoantibodies directed against various neural antigenic structures. SSN is characterised by autoantibodies against a neuronal intranuclear component called Hu (M. W. 35 to 40 kD), whereas in PCD these antibodies are directed against a Purkinje cell cytoplasmic component called (M. W. 34 and 65 kD). Neuroblastoma cell lines maintained in culture have been shown to contain neuronal antigens. We have demonstrated the presence of the Hu antigen in neuroblastoma cell lines such as SKN-SH, LAN-1 and IMR-32 by both immunocytochemistry and immunoblots of nuclear extracts. The Yo paraneoplastic antigen has been found to be expressed in HeLa cells. These methods may be used for screening of patients with suspected paraneoplastic disease and/or malignancy. Western blot analysis appears to be superior to immunohistochemistry alone. In our experience only 11 out of 122 SCLC patients were positive for the anti-Hu antibody, whereas 5 out of 5 patients with SSN/SCLC were positive, and all of the neurological controls were negative. The availability of cell lines expressing paraneoplastic antigens offers an easy diagnostic assay which may complement or replace conventional immunohistochemistry.