Background and Objectives: The mechanism for the destruction of a patient's own platelets in post-transfusion purpura (PTP) is unknown. In order to test the hypothesis that the destruction of autologous platelets in PTP is related to the presence of platelet antibodies with panreactivity, we investigated sera from patients with PTP. Materials and Methods:: Sera from 12 patients with PTP were investigated for platelet antibodies by platelet-ELISA and monoclonal antibody-specific immobilization of platelet antigen assay. Results:: During the thrombocytopenic phase, antibodies of IgG and lgM classes with pan-specificity against platelet GPIIb-IIIa, GPIb-IX and GPIa-IIa were found together with HPA alloantibodies. After recovery, the pan-specific antibodies disappeared or the extent of reactivity diminished, whereas the IgG HPA alloantibodies persisted. Conclusion: These findings provide evidence that transient panreactive antibodies may be responsible for the autologous platelet destruction in PTP.