Guillain-Barré syndrome (GBS) has two types; acute inflammatory demyelinating polyneuropathy (AIDP) and acute motor axonal neuropathy (AMAN). Recently, a nation-wide retrospective study showed that the rate of AMAN is higher in Japan than in western countries. A prospective study is now in progress. Elevated titers of serum anti-ganglioside antibodies are characteristic of GBS. Complement system has been shown to be involved in the anti-ganglioside antibody-mediated pathogenetic mechanisms. Some GBS patients have antibodies specific to a conformational epitope formed by two different gangliosides. Among such anti-ganglioside complex antibodies, anti-GD1a/GD1b IgG antibodies are shown to be associated with severe GBS requiring artificial ventilation. In contrast, antibodies highly specific to GD1b are associated with GBS with ataxia. Sensory ataxic neuropathy is induced by sensitization of rabbits with GD1b. An apoptotic mechanism has recently been shown to be involved in the pathogenesis of this animal model. Most of the patients with Fisher syndrome have anti-GQ1b IgG antibodies. Recent investigation on anti-ganglioside complex antibody showed that antibodies in Fisher syndrome can be subdivided into the three groups; GQ1b-specific, GQ1b/GM1-specific, and GQ1b/GD1a-specific. Research on antibodies to gangliosides and ganglioside complexes will provide us with a clue to develop a novel treatment of GBS.