Macrophages infiltrate peripheral nerves and may contribute to neural damage in the Guillain-Barre syndrome (GBS). We determined whether single nucleotide polymorphisms (SNP) in genes encoding macrophage-mediators are related to the susceptibility and severity of GBS. The frequencies of SNP in the TNFA, MMP9, IL10, and NOS2a genes did not differ between 263 GBS patients and 210 healthy subjects. The MMP9 C(-1562)T and TNFA C(-863)A SNP were associated with severe weakness and poor outcome, indicating that these SNP may be one of the factors predisposing to a severe form of GBS.