Serologic evidence of recent Campylobacter jejuni infection was found in 92 (45%) of 205 Japanese patients with Guillain-Barré syndrome (GBS), and 49% of those 92 patients also had antibodies to GM1. Sixteen independent clinical isolates from GBS patients were serotyped: 12 belonged to Penner's heat-stable (HS) O serotype HS-19, 3 to HS-2, and 1 to HS-4. Of the patients whose C. jejuni isolates belonged to HS-19, 80% had elevated anti-GM₁ antibodies. Although the correlation was significant between C. jejuni and GM₁ antibody, anti-GM₁ also was detected in 25% of patients without C. jejuni infection. Polymerase chain reaction-based restriction fragment length polymorphism analysis of an flaA gene showed that all HS-19 isolates, regardless of a GBS association, had an identical and distinguishable pattern, Cj-1, suggesting that HS-19:Cj-1 isolates are distinctive among C. jejuni isolates. Lectin typing showed that all GBS-associated HS-19 isolates contained terminal β-N-acetylglucosamine residues on their cell surface, but HS-19 isolates from patients with enteritis did not.