Seven children with chronic or intermittent and six with acute idiopathic thrombocytopenic purpura (ITP) were treated with large intravenous doses of polyvalent, intact immunoglobulin (Ig). In all patients the platelet count rose sharply within 5 days, but the initial response and the subsequent course varied from patient to patient. Among children with chronic ITP the initial response was more marked in splenectomised than in non-splenectomised patients. Among those with acute ITP the two who remained Ig dependent had a smaller initial response than the four patients who required no maintenance treatment. During the 90-110 days of observation five of six patients with chronic ITP could be maintained with Ig alone. No untoward effects of Ig therapy were observed.