Mean occlusion time in injured veins depends on VWF and FVIII. The time to form an occlusive thrombus was determined. (A) Mean occlusion time in WT, VWF^−/−, and VWF^+/− mice. None of the injured vessels in the VWF^−/− mice occluded during the 40-minute observation time, whereas all WT mice and VWF^+/− occluded. Eight of 9 venules of VWF^−/− mice infused with r-hu-FVIII did not occlude. (B) None of the injured vessels occluded during the 40-minute observation time in the FVIII^−/− mice (n = 5). The infusion of r-hu-FVIII normalized the occlusion time in all FVIII^−/− mice. (C) Mean occlusion time in IL4Rα/GPIbα-tg mice was 25 minutes compared with 19.5 minutes in the WT and all the IL4Rα/GPIbα-tg venules occluded at the site of injury.