Abstract: A polypeptide which is capable of inhibiting binding of von Willebrand factor (vWF) to platelets and comprising an amino acid sequence that corresponds to the amino acid sequence of that fragment of mature von Willebrand factor subunit having its amino terminus at about Cys.sup.509 and its carboxy terminus at about Cys.sup.695, said polypeptide comprising optionally a second and/or a third domain, the second domain corresponding to the amino acid sequence of that fragment of mature vWF subunit having its amino terminus at about Thr.sup.450 and its carboxy terminus at about Tyr.sup.508, or a subfragment or combination of subfragments thereof, and a third domain corresponding to the amino acid sequence of that fragment of mature vWF subunit having its amino terminus at about Asp.sup.696 and its carboxy terminus at about Gly.sup.