Desmopressin (DDAVP) affects haemostasis by the release of von Willebrand factor and coagulation factor VIII from endothelium. The aim of the study was to evaluate the results of DDAVP testing in paediatric patients with congenital bleeding disorders. Forty-one patients consisting of children with von Willebrand's disease (VWD, n = 26) and platelet function defects (PFD, n = 15) received DDAVP intravenously at a dosage of 0.3 μg/kg over 30min. FVIII activity (FVIII), von Willebrand factor antigen (VWF:Ag), collagen-binding activity (VWF:CB) and PFA 100® closure times (CT) were measured before, 60, 120 and 240min after DDAVP. In VWD, the VWF:Ag increased threefold until 60min and then it decreased continuously. Compared with baseline, VWF:Ag was significantly higher at 60 and 120min but not at 240 min. In contrast, in PFD, the peak of VWF:Ag was reached after 120min. Two hundred and forty minutes after DDAVP, the mean was still significantly elevated compared with baseline values. The course of VWF:CB corresponded to that of VWF:Ag. In patients with VWD and PFD, FVIII rose two- to threefold within 2h after DDAVP. CT in patients with VWD shortened markedly within 120min and then rose again. In all children with PFD, except one non-responder, the CT shortened within 240min after DDAVP. Two non-responders with VWD were identified by the failed increase of VWF:Ag, VWF:CB and by prolonged CT. Haemostatic effects of DDAVP differ interindividually and dependent on the coagulation disorder. DDAVP was effective in most, but not in all patients. DDAVP testing is recommended to determine the individual haemostatic response.