It is known that factor VIII related antigen (VIIIR:Ag) and plasminogen activator (PA) are synthesized in the vascular endothelial cells from which they may be released in response to certain stimuli such as venous occlusion (VO) or infusion of DDAVP (1‐desamino‐8‐D‐arginine vasopressin). To elucidate the possible association between these two factors we studied the response of factor VIII related activities and PA to VO and DDAVP (i.v. and i.n.) in 104 normal individuals, two patients with severe haemophilia A and 16 with various forms of von Willebrand's disease (vWd). Analysis of the results from each of the normal persons revealed a positive correlation between the maximal increase in plasma concentrations of VIIIR:Ag and PA after DDAVP. Furthermore, it could be demonstrated that some individuals responded repeatedly with either very high or very low F VIII and PA release. In four patients with severe vWd (no detectable VIIIR:Ag by an immunoradiometric method (IRMA)), DDAVP did not affect factor VIII related activities and no increase in PA was observed. Infusion of antihaemophilic factor (fraction I‐O, Kabi) prior to the administration of DDAVP failed to increase the PA levels. VO of the arms had no effect on PA in these patients. Four patients with moderate vWd (0.01 U/dl VIIIR:Ag by IRMA) developed fibrinolytic activity after DDAVP, however, within the lower limit of the normal range. In nine patients with mild or variant vWd (0.1 U/dl by IRMA), DDAVP caused increases both in factor VIII related activities and PA. The two haemophiliacs responded to DDAVP and VO with normal increases in PA and VIIIR:Ag. The combined data indicate that there is an association between the release of PA and factor VIII related activities in normals, haemophiliacs and patients with vWd.