Antecedent Campylobacter jejuni infection, detected by serologic tests, has been implicated in some acute immune polyneuropathies (AIP). Antibodies to Helicobacter pylori, C. jejuni, and GM1 ganglioside were measured in sera from 35 Chinese patients with AIP. Anti-GM1 antibodies were found in 54% of C. jejuni-seropositive, H. pylori-seronegative patients. In contrast, anti-GM1 antibodies were rare in sera that were either seropositive for both C. jejuni and H. pylori (P = .04) or seronegative for C. jejuni (P = .01). Motor axonal AIP was more common in the C. jejuni-seropositive, H. pylori-seronegative patients (82%) than in the bacterial antibody-negative group (38%). It was concluded that in AIP patients, C. jejuni-positive sera may be polyreactive, in that it may also react with H. pylori. In this situation, the specificity for either infection requires further validation. In contrast, sera with specific C. jejuni seropositivity are associated with both motor axonal AIP and selective serum IgG anti-GM1 antibodies.