Thrombus stability in VWF^−/− venules is restored by recombinant FVIII. The number of emboli (> 30 μm in diameter) generated before 19 minutes (mean occlusion time for WT mice) of injury was determined. Five times more emboli were observed in VWF^−/− mice compared with the WT. This was due to less FVIII, as reconstitution with r-hu-FVIII corrected the defect. Error bars indicate SEM.