GM2 ganglioside is a potential peripheral nerve antigen for neuropathy-associated autoantibodies. However little data are available on their pathogenic effects, if any. In this study we have screened both neuropathy-associated and control sera for anti-GM2 antibodies and subsequently used high titre sera for immunohistological and complement mediated cytotoxicity studies. We identified abnormally elevated anti-GM2 antisera in the normal population, as well as in patients with peripheral neuropathies and other neurological diseases. GM2 antibodies were either mono-reactive, cross-reactive with GMla, or cross-reactive with Gal-NAc-GMlb and/or GalNAc-GDla. All GM2 antisera from neuropathy subjects and normal controls bound to, and were capable of complement-mediated lysis of the NSC-34 cell line which expresses high levels of membrane-associated GM2. However, in immunohistological studies on human and rodent peripheral nervous system tissues, no specific binding was seen with GM2 antisera, either cross-reactive with GalNAc-GMlb and GalNAc-GDla, or with GMla. These data indicate that although GM2 antisera can lyse neural membranes containing GM2, this antigen(s) is not detectable by standard immunohistological techniques in human or rodent peripheral nerve. This raises doubts about their pathophysiological significance in human autoimmune neuropathy