Few reports exist on the influence of humoral immune responses, against microorganisms involved in infections preceding Guillain-Barré syndrome (GBS) and GM1, on clinical outcome. Nor is there any data on the relation between anti-Helicobacter pylori antibodies and prognosis in patients with GBS. To address these questions, we assayed and correlated serum anti-GM1 IgG and IgM and anti-H. pylori, anti-Campylobacter jejuni and anti-cytomegalovirus (CMV) IgG with duration of hospitalization of GBS patients and prognosis at discharge. Patients with anti-GM1 alone or associated with anti-H. pylori antibodies had significant longer hospitalization to reach a low clinical score at discharge than those without (P=0.004). A significant difference was also found for the association of anti-GM1 with anti-CMV antibodies (P=0.019). A weak but significant association of anti-GM1 and anti-C. jejuni antibodies with long hospitalization and worse prognosis at discharge was also found (P=0.02). The statistical significance increased when patients with anti-GM1 and anti-microorganism antibodies were compared with those displaying anti-H. pylori or anti-CMV only. These findings provide further evidence that the level of circulating anti-GM1 IgG plays a role in determining recovery from disability in GBS patients irrespective of other IgG against microorganisms causing infections preceding GBS.