Four different virus-inactivated factor VIII concentrates (Haemate P, Behring; Profilate, Alpha, FVIII-VHP-vWF, CRTS), near-pure von Willebrand factor (Facteur Willebrand, CRTS) or one recombinant FVIII preparation (Recombinate, Baxter) were given to one or more patients with different forms of von Willebrand's disease. Duke bleeding time, VIII:C, vWF:Ag, RC of activity, and the multimeric pattern of plasma vWF were monitored. Both Duke bleeding time and the multimeric pattern were normalized after treatment with Haemate P, FVIII-VHP-vWF, or Facteur Willebrand, and to a lesser extent after Profilate. Except in one case, the reduction in bleeding time lasted longer after Haemate P than after the other concentrates. Recombinate had no effect on primary hemostasis, and the half-life of VIII:C was very short. If prompt hemostasis is required, and when pharmacological correction of the defect is impossible, we recommend a concentrate containing both FVIII and the full complement of vWF multimers, but for prophylactic treatment pure von Willebrand factor may be used.