Intravenous immunoglobulin (IVIG) may be considered first-line maintenance therapy for idiopathic thrombocytopenic purpura (ITP) because it has been proven to be the least toxic. In a study of 25 children with acute ITP, treatment with IVIG maintained platelet counts above 40,000/mm3 in all of the children. After 1 year, none of these patients required further therapy. In another study group of 25 pediatric patients with chronic ITP, treatment with IVIG circumvented splenectomy in 60% of the cases. The therapeutic regimens for adults and children are described, as is a strategy to overcome IVIG resistance. Experience with IVIG in hemolytic anemia and neutropenia are discussed. The mechanism of action is explored in some detail, specifically as it relates to reticuloendothelial system (RES) Fc receptor blockade and suppression of antiplatelet antibody synthesis.