Intravenous immunoglobulin is not only a dramatic clinical therapy, but it is also extremely interesting in regard to mechanism of action. The high cost of therapy limits its application, yet it appears to be equal to or perhaps slightly more effective than corticosteroids as a treatment of ITP and is far less toxic with prolonged use. The appropriate place for its exact use remains to be determined but probably includes patients urgently requiring rapid platelet increases (in conjunction with steroids), treatment of immunocompromised patients, and treatment of chronic patients, either children to avoid splenectomy or adults with severe disease after splenectomy. Controlled trials to resolve these clinical questions are urgently needed. Existing studies on its mechanisms of actions are very interesting and have furthered our understanding of the pathophysiology of ITP. Although future work may lead to further applications, initial enthusiasm for the use of IVGG in the treatment of other autoimmune diseases with the exception of myasthenia gravis has been limited by subsequent clinical experience.