Summary:The von Willebrand factor (vWf) activity, as measured by the ristocetin co‐factor (vWf:RCo) and collagen binding (vWf:CBA) assays, declined progressively in standard blood units stored at 4°C after a 2‐day storage period. This loss of activity was accompanied by a loss and degradation of high molecular weight (HMW) vWf multimers. In studies using a paired design, filtration of blood with a high efficiency leucocyte‐removal filter, prior to storage at 4°C, led to significantly improved maintenance of vWf:RCo and vWf:CBA compared with unfiltered units (P,<0·01 after 8 days). Loss and degradation of HMW vWf decreased when blood was filtered prior to 4°C storage. Filtration had no effect on vWf‐associated activities when blood was stored at 22°C for 10 days.These results indicate that part of the storage lesion of vWf in banked blood is due to leucocyte‐mediated removal and degradation of HMW vWf. This has implications when specifying plasma for the production of vWF concentrates and may also play a role in the haemostatic lesion associated with massive transfusion o