We describe an outbreak of Campylobacter jejuni enteritis involving three family members of whom one developed Guillain-Barré syndrome (GBS). The patients' serum reacted strongly with several gangliosides and with the lipopolysaccharide (LPS) fractions from the C. jejuni strains isolated from his family members. Only low titer anti-ganglioside antibodies were found in his siblings. HLA-typing did not indicate a locus associated with auto-antibody production. Comparing the immune response in GBS patients and C. jejuni enteritis patients can be of great value in determining the additional factors that lead to post-Campylobacter GBS. Ganglioside mimicry alone is necessary but not sufficient for the induction of anti-ganglioside antibodies. Other susceptibility factors are required to induce an anti-neural immune response.