Some patients developed Guillain-Barré syndrome (GBS) after the administration of bovine gangliosides. Patients with GBS subsequent to Campylobacter jejuni enteritis frequently have IgG antibody to GM1 ganglioside. Fisher's syndrome (FS), a variant of GBS, is associated with IgG antibody to GQ1b ganglioside. We showed the existence of molecular mimicry between GM1 and lipopolysaccharide (LPS) of C. jejuni isolated from a GBS patient, and that between GQ1b and C. jejuni LPSs from FS patients. Several lines of evidence suggest a pathogenic role for anti-ganglioside antibodies. Some patients developed sensorimotor polyneuropathy after anti-GD2 antibody administration. Anti-GM1 antibody can block motor nerve conduction. The molecular mimicry between infectious agents and gangliosides may function in the production of anti-ganglioside antibodies and the development of GBS and FS. Anti-GQ1b IgG antibody is detected also in Bickerstaff's brainstem encephalitis and acute ophthalmoparesis, which suggests that these conditions are categorized as autoimmune diseases related to FS. Since a tryptophan-immobilized column effectively adsorb anti-GQ1b IgG antibody, immunoadsorption with the column should be considered as an alternative form of plasmapheresis for the anti-GQ1b IgG antibody syndrome.