The present invention provides, inter alia, transgenic non-human animals, such as transgenic mice. The animals contain in their genome a polynucleotide encoding a von Willebrand factor (VWF) polypeptide, which polypeptide forms a thrombus when in the presence of human platelets. Nucleic acid sequences and vectors for generating the transgenic non-human animals, and methods for using the transgenic non-human animals are provided as well. Chimeric VWF proteins are also provided.
