We developed testing kits for anti-GM1 and anti-GQ1b IgG antibodies and examined their utilities in supporting the diagnosis of Guillain-Barré syndrome (GBS) and Fisher syndrome (FS). Anti-GM1 antibody was detected in 49% of 95 patients with GBS and in 5% or less of disease and normal controls. Anti-GQ1b antibody was detected in 85% of 55 patients with FS, whereas in none of the controls. Eight GBS patients, in whom anti-GM1 IgG antibody was judged negative using the kit, were found to have other anti-ganglioside IgG antibodies. Four of them showed ophthalmoplegia and had anti-GQ1b IgG antibody. Detection of anti-GM1 IgG antibody in GBS and of anti-GQ1b IgG antibody in FS within one week after the disease onset were significantly more frequent compared to albuminocytologic dissociation in the cerebrospinal fluids (GBS, 58% vs 32%; FS, 89% vs 20%). These findings indicate that our testing kits are useful for supporting the early diagnosis of GBS and FS.