We examined serum anti-cytomegalovirus (CMV) and anti-ganglioside antibodies by ELISA in 51 patients with Guillain-Barré syndrome (GBS), and titers were compared with those from 47 normal and 74 disease controls. Three GBS patients with IgM anti-CMV antibodies had high titers of IgM and IgG anti-GM2 antibodies. The other GBS patients without IgM anti-CMV antibodies, and the normal and disease controls except one of 6 non-GBS patients with acute CMV infections had no anti-GM2 antibodies. The titers of anti-GM2 antibodies decreased on absorption with CMV-infected cells. These findings suggest that anti-GM2 antibodies are associated with acute CMV infections in GBS patients.