To define structural rearrangements occurring during interaction between PAI-1 and its target proteinases we have raised monoclonal antibodies against the PAI-1/t-PA complex.     ///    Thirteen out of 401 monoclonal antibodies reacted preferentially with the PAI-1/t-PA complex as compared to free PAI-1 or free t-PA.     ///    Detailed characterization revealed the presence of two non-overlapping neoantigenic epitopes in the PAI-1/t-PA complex. 