A highly purified von Willebrand factor (vWf) concentrate with low factor VIII (FVIII) content was tested to evaluate its biological effects in five patients with severe von Willebrand disease (vWd). The patients were infused with a single dose of this product corresponding to ˜65 IU vWf:RCo and ˜11 IU FVIII:C/kg and were followed up for 48h. The plasma levels of FVIII and vWf and the multimeric pattern of vWf were determined before and 1,3,6, 12, 24 and 48h after infusion. In all patients the recovery (93 ± 14%) and half-life (13 ± 1h) of vWf were consistent and normal and sustained FVIII levels were attained. In four patients both the duration and the volume of shed blood were measured after one incision with a standardized template method of bleeding time (BT). The duration of bleeding was completely corrected in two out of the four patients and partially corrected in the other two while the volume of shed blood was completely corrected in three patients and partially corrected in the fourth. However, the time for correction of both BT parameters was variable between patients. These data indicate that the vWf concentrate can correct the quantitative defects related to plasma vWf deficiency in vWd patients whereas the effect on template BT is less reproducible.