Plasma VWF is the major determinant to control bleeding in a tail clip bleeding assay. Five mm of the tail of WT (n = 15), VWF KO (n = 14), VWF PLT chimeric (n = 16), and VWF EC chimeric (n = 9) mice was removed. Subsequent tail bleeding in pre-warmed saline was monitored and the time needed to stop the bleeding was recorded. If bleeding did not end within the first 10 minutes, the experiment was ended with a recorded bleeding time of 600 seconds. ns, not statistically significant. ***P < .001; ****P < .0001.