 This study will examine the safety, tolerability, and efficacy of the humanized monoclonal antibody Rituximab to induce a clinical and serological remission in patients with IgM-anti-glycoconjugate antibody-mediated demyelinating neuropathy. Rituximab is a monoclonal antibody specific for the common B cell antigen CD20. Its administration depletes pre-B and mature B lymphocytes without altering neutrophils or hematopoietic stem cells. In humans with indolent B cell lymphomas, Rituximab can be safely administered, is well tolerated, promotes selective B cell depletion and lowers the serum IgM levels. Preliminary experience in some patients with demyelinating polyneuropathy and IgM-anti-glycolipid antibodies has shown that Rituximab was beneficial in improving the patients symptoms and reducing the anti IgM antibody levels. In the present study we will examine in a placebo randomized trial the efficacy of Rituximab in patients with polyneuropathy related to IgM-anti-glycolipid antibodies. Twenty-six patients will be randomized to receive placebo or Rituximab given at four weekly intravenous infusions of 375 mgM2. The primary outcome will be based on changes in the monthly measurements of the neuropathy scores. The fine specificities of the IgM antibodies to various glycoconjugates or differences in the affinity binding to various antigens in neural membranes will be explored before and after treatment. It is anticipated that the study will: a provide a new, immune-based and target-oriented therapy for patients with this neuropathy and b examine the pathogenic role of these antibodies in the cause of the disease. 