Unlike CNS myelin, human peripheral nerve myelin has the acidic glycosphingolipids sialosyl paragloboside (SPG), sialosyl lactosaminyl paragloboside (SLPG), and sulfated glucuronyl paragloboside (SGPG). To elucidate the pathogenesis of Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating neuropathy (CIDP), we investigated the autoantibodies to peripheral nerve molecules in patients with these diseases and compared the frequency of the autoantibodies with that of autoantibody to GM1 which is present in both the CNS and PNS. The report of Sheikh et al. (Ann. Neurol. 1995; 38: 350) that Campylobacter jejuni bears the SGPG epitope led us to study whether sera from patients with GBS subsequent to C. jejuni enteritis have anti-SGPG antibody; but, high anti-SGPG antibody titers were not found in the GBS patients from whom C. jejuni was isolated. Although the frequency of the anti-SPG, anti-SLPG and anti-SGPG antibodies were lower than that of the anti-GM1 antibody in GBS, 5 patients with demyelinating GBS had high IgG anti-SPG antibody titers. IgG anti-SPG antibody may function in the development of demyelinating GBS. We found that 6 CIDP patients had elevated IgM anti-SGPG antibody titers. Immunoelectrophoresis failed to detect IgM M-protein in 3 of the patients. IgM anti-SGPG antibody could be a diagnostic marker for a subgroup of CIDP with or without paraprotein.