The natural variety of IgG isotype function suggests the use of IgG for therapeutic purposes. Whereas the clinical efficacy of substituting IgG through the i.m. and i.v. routes in combating infectious complications has long been known, the usefulness of i.v. IgG in comparatively high doses for the treatment of autoimmune disease states has been discovered serendipitously upon observing normalized platelet concentrates in IVIG-treated patients with immune thrombocytopenias. In such situations, a network of regulated humoral immune capacity, inherent to the large plasma pool of healthy donations, is conferred on the recipient and helps to reestablish homeostasis of deficient immune function. The indications for IVIG in diseases with abnormal immunity are rarely first choice but must be considered when conventional and cheaper options have failed. This is the case with the following diseases: idiopathic thrombocytopenic purpura, myasthenia gravis, Guillain-Barré disease, systemic lupus, rheumatoid arthritis, Evans syndrome, auto- and alloimmune cytopenias, polymyositis/dermatomyositis as well a haemorrhagic syndrome due to inhibitors against clotting factor VIII. In order to achieve synergism, a combination of IVIG with other therapeutic measures such as immunosuppressive agents, plasma exchange and/or immunosorption may be advisable. With such combinations, particularities in disease dynamics may be taken into account acceptable dosage recommendations for the treatment of autoimmune disease are not always available. The mechanisms of action of successful IVIG infusions are not yet completely understood. Those experimentally identified include: neutralization of autoimmune induction mechanisms; activity as anti-idiotypic agents; down-regulation of the Fc receptor apparatus, up-regulation of interleukin-1 receptor antagonist; deviation of complement activation to non-inflammatory targets and modulation of superantigens.