IDIOPATHIC thrombocytopenic purpura (ITP) is a disease entity characterized by a decrease in the circulating platelets despite an increase in megakaryocytes seen in the marrow. There is a concomitant bleeding tendency, but the precise pathophysiological cause or etiology is unknown. The disease is distinguished from secondary thrombocytopenic purpura almost by the process of exclusion; there is no history of a preceding infection and toxic exposure to such agents as quinidine or arsenicals and allergic responses are absent. Usually, splenomegaly is not present. Although the term idiopathic implies a lack of knowledge of the basic mechanisms involved, much is known about this disease process and its possible pathophysiologic genesis. Acute cases occur primarily in children and may be of viral origin; the chronic refractory cases are seen in all decades of life. Although it is not the purpose of this paper to discuss hematologic production (Harrington) versus sequestration of platelets or