Antibodies specific for a complex of gangliosides GD1a and GD1b (GD1a/GD1b) were found in sera from eight of 100 patients with Guillain-Barre syndrome (GBS) by the use of enzyme-linked immunosorbent assay and thin-layer chromatogram immunostaining. Those sera also had antibody activities to such ganglioside complexes as GD1a/GM1, GD1b/GT1b, and GM1/GT1b but had little or no reactivity to the each isolated antigen. Clustered epitopes of the ganglioside complex in the plasma membrane may be targeted by such an antibody, and interaction between the antibody and ganglioside complex may induce the neuropathy.