The susceptibility of von Willebrand factor /vWF/ to digestion by human neutrophil cathepsin G in highly purified FVIII/vWF concentrate /BHS/ and in cryoprecipitate has been studied. In contrast to human neutrophil elastase, cathepsin G inactivates and degrades vWF not only in BHS but also in cryoprecipitate. Fibrinogen added in excess to purified FVIII/vWF concentrate does not protect vWF against cathepsin G proteolysis. Biological significance of this phenomena are discussed.