SummaryIn this paper the antiplatelet and antithrombotic activity of Dipyridamole is described. In in vitro tests the effect on platelet adhesion was found to be more pronounced than that on different types of aggregation.In in vivo models a good and long lasting inhibiting effect on primary haemostasis was seen in mice. An antithrombotic effect was achieved in a thrombus formation test in rats. The dose of Dipyridamole used in these in vivo experiments was only 10mg/kg orally.