Plasma exchange involves non-selectively removing plasma components that are potentially pathogenic in immune-mediated diseases from a patient's blood. Intravenous immunoglobulin used for therapeutic purposes are pooled human immunoglobulins derived from the plasma of 10000-100000 healthy donors. The major component of intravenous immunoglobulins (IVIg) preparations is IgG; very small amounts of other immunoglobulins, immunoglobulin fragments, and other smaller plasma proteins are also present. IVIg affect several components of the immune system and have been used successfully in the treatment of several neuroimmunological disorders. IVIg therapy has been evaluated both as a treatment of acute demyelinating relapses as well as a maintenance therapy to alter the disease course in adult patients with multiple sclerosis (MS). This chapter focuses on studies pertaining to the treatment of acute relapses. Plasma exchange might be an effective and relatively well-tolerated treatment option for severe demyelinating relapses in MS patients.