Abstract: The invention relates to the adhesion of platelet GpIb? to strand ?3 of domain A1 of von Willebrand factor (vWF), the strand ?3 comprising amino acid residues at amino acid position 560-566 and/or a functional part or equivalent thereof, the platelet GpIb?, the GpIb? region comprising an amino acid sequence corresponding to a beta-switch loop of platelet GpIb?, comprising amino acid residues at amino acid position 227-242 and/or a functional part or equivalent thereof. The invention provides a method of interfering with adhesion of blood platelets to vWF that includes modulating adhesion. The invention further provides proteinaceous compounds, antibodies, medicaments and pharmaceutical compositions to that end. The invention also provides means and methods to increase platelet adhesion by topical application of a compound increasing platelet adhesion.