In the last decade, a set ofantineuronal antibodies has been found in serum and cerebrospinal fluid (CSF) of patients suffering from neurological paraneoplastic disorders. Except for rare and less wellstudied antibodies, 3 types of antibodies associated with a typical clinical picturc are most frequcntly found. Patients with paraneoplas-tic encephalomyelitis manifesting itself as limbic encephalitis, brain-stem or ccrebellar syndrome and ataxia associatcd almost regulary with small cell bronchial carcinoma have antibodies against 35-to 40-kD neuronal nuclear proteins called anti-Hu (ANNA-1). Patients with paraneoplastic cerebellar degeneration show antibodies called anti-Yo (PCA-l), reacting with 34-and 62-kD proteins in Purkinje cell cytoplasm. This antibody mostly is related to carcinoma of the breast or female genital tract. The third group represents the paraneoplastic opsoclonus syndrome that is seen in children with neuroblastoma or adults with lung and predominantly breast cancer [1–3]. Patients presenting with opsoclonus-myoclonus and breast cancer have antibodies called anti-Ri (ANNA-2), directed against 55-and 80-kD neuronal nuclear proteins [4, 5]. One Of the Ri antigens, called Nova I, is homologeous to an RNA-binding protein and is specifically expressed in the developing motor system [6]