1-Deamino-8-d-arginine vasopressin (D.D.A.V.P.) infusion causes a marked increase in factor-VIII (antihaemophilic-factor)-related properties in patients with moderate and mild haemophilia and von Willebrand's disease (vWd). The possibility was therefore evaluated that such an autologous factor-VII response might be haemostatically effective, allowing patients to undergo surgery without plasma concentrates. 0.3 microng/kg of D.D.A.V.P. given before dental surgery and repeated in the early postoperative period was followed by a two to three fold rise in factor-VIII coagulant activity (VII C.A.) in four patients with moderate and mild haemophilia. In two, there was no abnormal bleeding after dental extraction, whereas plasma concentrates were necessary to control oozing from the sockets in the remaining two patients. A higher D.D.A.V.P. dosage (0.4-0.5 microng/kg) in patients with higherstarting VII C.A. (9% or more) was followed by a more marked response (four to six fold). VII C.A. levels up to 100% of average normal were achieved and dental extraction and major surgery (such as cholecystectomy, thoracotomy, and two tonsillectomies) were carried out successfullly in six patients with mild haemophilis and in two with vWd. The mean half-life of autologous VII C.A. was 9.4 h (range 7.5-11.6). Plasma and urine osmolality showed no consistent variation after drug administration. Thus D.D.A.V.P. appears a promision pharmacological alternative to plasma concentrates in the management of some patients with haemophilis and vWd.