Aim: Idiopathic thrombocytopenic purpura (ITP) is one of the most commonhemorrhagenic diseases. The recent research results about the humoral immunitymechanism of ITP showed that platelet autoantibodies found in the plasm as well ason the platelet of the patients with ITP. These autoantibodies are known to react withthe membrane glycoprotein complexes(GpIIb/IIIa. GpIb,and so on )on the plateletsurface and some have been shown to bind to the antigens on the megakaryocyte,so that it results in mature platelet destruction by the reticuloendothelial system orinhibition of platelet production.Up to now, the valuable method of serologic testingof patients with ITP has never been estabIished. The purPose of this study wll be toexplore the establishment of a novel hematologic diagnostic method of ITP bydetecting plasm antiplatelet autoantibodies and platelet associated autoantibodies in thepatients of ITP. Method: Two methods were used in this study to test plasmalltiplatelet autoantibodies and platelet associated autoantibodies of 2l cases with ITP,l8 cases with secondary thrombocytopenic purPura(STP) and l5 normal persons.(l)Plasm antiplatelet autoantiobodies were detected by using immunocytochemicalmethod (Streptavidin biotin compIex, SABC) with the smearing of Dami celI culturedin our laboratory. The principle of the method is that the membrane surface markers(GPIlb/IIIa. GpIb and vWF)of Dami celI bind Wth plasm antiplqtelet autoantibodies -which could react with biotinylated sheep-antihuman lgG(b-SAHG), and then biotinconjugates strepavidin-alkaline phosphatase Which could catalyze the coloratidn ofsubstrate, fast-Red. The strength of the reaction relates to the quantity of plasmantiplatelet autoantibodies. (2).Platelet associated autoantibodies (PAIgG. PAIgM.PAIgA) were detected by a competitive enzyme-linked immunosorbant assay(CELISA).The principle is that Ig coated in microtiter test plate competed with PAIgof platelet fOr combining with enzyme-conjugated antihuman Ig.The strength of thereaction is inverse ratio with the quantity of PAIg. Results: (l).The results ofimmunocytochemical assay showed that some red precipitation granuIes wereobserved in Dami cells. It was obvious that the red precipitation granules in ITPpatients were much more than ones in normal persons and secondarythrombocytopenic purpura patients.The stained cells were analysed by the method ofsemi-quantitative analysis provided by CMIAS-8 (color medical image analysissystem). The results of the photo analysis indicated that the area density of positivecells (the total area of positive cells/the total area of stat field) and the count density ofpositive cells (the total quantity of positive eeII/the total area of stat field) of ITPgroups significantly increased compared with the controI groups(P <0.05). (2).Theresults of CELISA ghowed that aIl kinds of PAIg with ITP were increased. The Ievel ofPAIg had the minus correlation with the platelet counts and it was signiflcantlydifferent from both resuIts of normal subjects groups and STP groups(P<0.05).Conclusion: The both plasm antiplatelet autoantibodies and platelet associatedamoantidobies were present in most cases with ITP (l7/l2 cases,80.9%) and the unitedtesting the plasm antiplateIet autoantibodies. PAIgG. PAIgM. PAIgA could increasethe positive diagnosis rate of ITP by l00%.Among the above four assays, theimmunocytochemical method with smearing Dami cells was simple and of highspecificity. Our data indicate that the immunocytochemical method may be clinicalpracticable in diagnosing patients with ITP and would proInote the further research ofpathogenetic mechanism of ITP.