Intravenous immunoglobulin (IVIg) pooled from healthy human volunteers has a role in several immunomodulating mechanisms which may affect the pathogenesis of multiple sclerosis. Modulation of the disease course by IVIg is achieved both by limiting the inflammatory process and by enhancing remyelination. Clinical evidence of the effects of IVIg in multiple sclerosis is based on the results of several trials demonstrating the beneficial effects of IVIg on the relapse rate and on neurological disability. Brain magnetic resonance imaging studies support the clinical results by showing a decrease in both the disease burden and the appearance of new lesions. Preliminary results have demonstrated an improvement in the parameters of isometric muscle testing, chronic optic neuritis and the prevention of postpartum relapses. However, design and sample size limitations require larger controlled studies to substantiate these reports. Integrating the accumulating experimental data with clinical experience will assist in defining the specific mechanisms by which IVIg suppresses the disease process and clarify the future indications for IVIg treatment in multiple sclerosis.