Immunoglobulins have a variety of actions in dysimmune disorders. In neurological conditions such as the dysimmune neuropathies and multiple sclerosis, immunoglobulins are thought to exert a twofold effect: an immunomodulating action and a positive action on remyelination. We outline well recognized immunomodulator actions including the suppression of antibody production and neutralization of pathogenic antibodies, action on T lymphocytes and endothelial cells, modulation of complement proteins, and modulation of the expression of Fc gamma receptors on the surface of macrophages. Along with these actions in dysimmune disorders of the central and peripheral nervous systems, recent studies have provided evidence for an action on remyelination. In cultures of oligodendrocytes or myelinating cocultures of rat embryo brains, we have noted a direct action of immunoglobulins (tégéline) on myelination of the central nervous system. Our investigations have also indicated that immunoglobulins have an action on myelination of the peripheral nervous system. We employed the experimental acute neuritis model as well as in vitro models such as cultures of embryonic dorsal root ganglia and isolated Schwann cells. Interestingly the typical IgM immunoglobulins seemed more active than typical IgG ones. This observation may prompt new therapeutic options.