We studied genetic polymorphisms in the tumor necrosis factor (TNF) region in 81 Japanese patients with Guillain-Barré syndrome (GBS) and 85 controls. A significantly higher frequency of the 100-base pair (bp) (TNFa2) allele of the TNFa microsatellite marker, which is associated with high TNF alpha production, existed in Campylobacter jejuni-positive (Cj+) GBS patients than in controls, suggesting the involvement of a genetic predisposition to high TNF alpha secretion in the development of C. jejuni-related GBS.