The invention relates to the development of an animal model for testing various agents in the treatment of a clotting disorder. More specifically, the invention relates to the use of ultra-large molecular weight multimers of von Willebrand factor (VWF) in various mouse strains to induce thrombotic thrombocytopenic purpura (TTP)-like symptoms for the development of a mouse model of TTP. The invention also provides methods for generating such animal disease models and screening methods for identifying biologically active compounds which are effective in the treatment of TTP.