Platelet depletion decreases leukocyte rolling in Adamts13^−/− mice. The number of leukocytes rolling per minute was determined by phase-contrast intravital microscopy. Platelet depletion resulted in decreased leukocyte rolling in Adamts13^−/− mice compared with nondepleted in Adamts13^−/− mice but not in Adamts13^+/+ mice, indicating that platelets are part of the mechanism that results in increased leukocyte rolling in Adamts13^−/− veins. Data represent the mean ± SEM.