The utility of an enzyme linked immunoassay for the detection of platelet alloantibodies to isolated platelet glycoproteins employing commercially available monoclonal antibodies was studied. The authors established the usefulness of the assay for antibodies to platelet alloantigens (APAA) by testing its sensitivity and specificity under different conditions and using a variety of alloantibodies from patients with immune mediated thrombocytopenia. The authors were able to specifically detect a variety of antibodies to platelet alloantigens on different platelet glycoproteins. These antibodies had specificity for HPA-1a (PIA1), HPA-3 (Bak) and HPA-5 (Br). These results show that the APAA is easily adaptable for routine diagnostic testing in hospital laboratories using commercially available monoclonal antibodies and for the diagnosis of alloimmune mediated thrombocytopenic conditions.