We describe a 13-year-old girl with chronic idiopathic thrombocytopenic purpura who showed a response to a high-dose intra venous gammaglobulin combined with prednisolone, without any response to a high-dose intravenous gammaglobulin therapy alone. This observation suggests the additive or multiplicative effects of these two drugs. Platelet-associated IgG level showed an inverse correlation with the number of platelets.