A test is needed of which the score is low in case of haemorrhagic tendency and high in case of thrombotic tendency. Emerging evidence shows that thrombin generation is a promising candidate. Recently it became possible to measure the course in thrombin concentration in clotting blood or blood plasma in an simple way suitable for application in a routine clinical setting. It appears that the amount of thrombin developing in clotting blood or blood plasma is a better measure for thrombotic- or haemorrhagic tendency than any variant of the clotting time and that thrombin generation is a universal test for the effect of antithrombotic drugs.