It is now emerging the new concept that the antibodies from some patients with Guillain–Barré syndrome (GBS) recognize an antigenic epitope formed by two different gangliosides, a ganglioside complex (GSC). We prepared the dimeric GM1–GD1a hybrid ganglioside derivative that contains two structurally different oligosaccharide chains to mimic the GSC. We use this compound to analyze sera from GBS patients by high-performance thin-layer chromatography immunostaining and enzyme-linked immunosorbent assay. We also synthesized the dimeric GM1–GM1 and GD1a–GD1a compounds that were used in control experiments together with natural gangliosides. The hybrid dimeric GM1–GD1a was specifically recognized by human sera from GBS patients that developed anti-oligosaccharide antibodies specific for grouped complex oligosaccharides, confirming the information that GBS patients developed antibodies against a GSC. High-resolution 1H-13C heteronuclear single-quantum coherence-nuclear overhauser effect spectroscopy nuclear magnetic resonance experiments showed an interaction between the IV Gal-H1 of GM1 and the IV Gal-H2 of GD1a suggesting that the two oligosaccharide chains of the dimeric ganglioside form a single epitope recognized by a single-antibody domain. The availability of a method capable to prepare several hybrid gangliosides, and the availability of simple analytical approaches, opens new perspectives for the understanding and the therapy of several neuropathies.