1-Deamino-8-.D-arginine vasopressin (DDAVP) was administered to 3 patients with spontaneous factor VIII inhibitors. In 2 patients with baseline factor VIII levels above 1 %, a marked increase of factor VIII activity after DDAVP infusion could be observed. No rise of factor VIII activity after DDAVP was seen in the 3rd patient with a baseline factor VIII level of less than 1 %. Daily infusion of DDAVP resulted in a reduction of the efficacy, but the full effect could be retained when DDAVP was given at 48-hour intervals. The effect of DDAVP infusion on factor VIII levels in the 2 responding patients was superior to the treatment with 30 U/kg factor VIII concentrate and approximately equivalent to infusion of 45 U/kg factor VIII concentrate. DDAVP may be a useful and less expensive treatment for patients with acquired factor VIII inhibitors and a baseline factor VIII level of more than 1 %.