Described herein are polypeptides comprising at least one single domainantibodydirected against von Willebrand Factor (vWF) for the treatment of conditionswhich require amodulation of platelet-mediated aggregation. A further aspect comprisesmethods ofproduction of said polypeptides, methods to coat devices with suchpolypeptides used inmedical procedures (e.g. PCTA, stenting) and kits for the diagnosis ofdiseases related toplatelet-mediated aggregation.