It has recently been shown that the ultralarge platelet-recruiting VWF strings formed immediately at exocytosis from endothelial cells may be anchored to the cell surface by an interaction with the integral membrane protein P-selectin. This finding of a new binding partner for VWF immediately raises the question of which domains of VWF bind to P-selectin. We have exploited the fact that expression of VWF in HEK293 cells triggers the formation of Weibel-Palade body-like structures that can recruit P-selectin. A suitably modified version of this assay using co-expressed truncations of VWF together with P-selectin variants in HEK2193 cells allowed us to determine which domains of VWF would recruit P-selectin within a physiologically appropriate intracellular environment. Confirming the results of such a cellular assay by conventional co-immunoprecipitation, we conclude that the lumenal domain of P-selectin interacts with the D'-D3 domains of VWF.