Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disorder characterized by thrombocytopenia due to antiplatelet autoantibodies. It has been demonstrated that the platelet glycoprotein (GP) IIb-IIIa and/or GPIb-IX are major target antigens for the autoantibodies in this disorder. Diagnosis of ITP has usually been based on clinical criteria. However, development of reliable immunological techniques enable us to make a diagnosis of "autoimmune thrombocytopenic purpura" in some patients. In this paper, we review the immunological techniques such as immunoblot assay, immunoprecipitation assay, and modified antigen capture ELISA, and discuss the clinical significance of the detected anti-GPIIb-IIIa auto-antibodies.