The authors studied immunoglobulin G (IgG) Fc receptor (FcgammaR) IIA, IIIA, and IIIB polymorphisms in 62 patients with Guillain-Barré syndrome (GBS) and in 89 healthy controls. The FcgammaR genotypes and allele frequencies did not differ significantly between the patients with GBS and the controls. Patients homozygous for the FcgammaRIIIB neutrophil antigen (NA) 1 allele had a significantly less severe disease than patients heterozygous or homozygous for the NA2 allele. The FcgammaRIIIB NA1/NA1 genotype has high affinity for IgG1 and IgG3, and clearance of circulating autoantibodies and immune complexes may therefore be of importance in the pathogenesis of GBS.