Abstract Certain species of anti-ganglioside antibodies are associated with specific clinical features in various neurologic diseases. Serum autoantibodies to these minor gangliosides were investigated in a number of neurological diseases in order to examine the biological functions of GD1α and GQ1β. Eleven patients with Guillain-Barré syndrome had remarkably high IgG anti-GD1α antibody titers, but no GD1α was detected in human peripheral nerve. An absorption study showed that IgG anti-GD1α antibodies from eight of the 11 patients were significantly absorbed by GD1a and GM1b, indicative that the IgG anti-GD1α antibodies cross-react with GD1a and GM1b. Both GD1a and GM1b have been reported to be target molecules for serum antibodies in certain patients with Guillain-Barré syndrome. GD1α may induce the production of IgG anti-GD1α antibody which cross-reacts with GD1a or GM1b, and subsequently functions in the development of Guillain-Barré syndrome. The IgGs from six patients with Fisher’s syndrome who had the anti-GQ1β antibody had anti-GQ1b activity as well. All the patients had external ophthalmoplegia, but no GQ1β was detected in the human oculomotor nerve, further evidence that GQ1b, not GQ1β, is the molecule targeted by the autoantibody in Fisher’s syndrome.