A review of the pathological basis of multiple sclerosis is presented to see whether the many immunological effects if IVIg may exert some benefit and at what level. This is probably due to the wide spectrum of interactions between IVIg and the immune system, which are analyzed in this review. Macrophage Fc receptor saturation and block, anti-idiotypic effect, reduction of endothelial cell activation and superantigen-neutralizing antibodies are probably involved in the action of IVIg in dysimmune demyelinating diseases. Furthermore, IVIg promote remyelination in virus-induced experimental encephalomyelitis. Trials on IVIg in MS demonstrated a reduction of relapse rate (RR) and appearance of gadolinium-enhancing lesions on magnetic resonance imaging. Furthermore IvIg are regarded as a promising treatment to reduce RR in post-partum period. However, studies on secondary-progressive MS failed to demonstrate an IVIg effect on disability and IVIg failed to improve stabilized visual and motor deficits in two large trials.