We report a study undertaken to test the biological effect of intranasal 1-deamino-8-D-arginine vasopressin (DDAVP) and its efficacy in the treatment of bleedings in patients with mild factor VIII deficiency. The biological study was carried out in 20 patients: an increase of factor VIII:C and von Willebrand factor antigen levels was observed after inhalation of DDAVP at average post/pre inhalation ratios of 2.80 and 1.72, respectively. No relevant alterations of fibrinolysis were noted. In fact, we only observed a simultaneous increase of tissue plasminogen activator and plasminogen activator inhibitor, without modification of D-dimer. In 10 cases intranasal DDAVP has been used in the prevention or in the treatment of bleeding complications: no bleedings were observed.