By the use of a fluorogenic thrombin substrate and continuous calibration of each individual sample, it is now possible to obtain a thrombin generation (TG) curve (or thrombogram) in plasma, with or without platelets, in an easy routine procedure at high throughput and with an acceptable experimental error (<5%). Evidence is growing that the parameters of the thrombogram, and notably the area under the curve (endogenous thrombin potential, ETP), are useful in assessing bleeding- or thrombotic risk and its modification by antithrombotic- or haemostatic treatment. Available data strongly suggest that conditions (congenital, acquired, drug-induced) that increase TG all cause a thrombotic tendency and that conditions that decrease TG prevent thrombosis but, beyond a limit, cause bleeding. Diminution of TG is a common denominator of all antithrombotic treatment, including anti-platelet drugs. The thrombogram can also be used as a tool in the search for new antithrombotics and reflects the haemorrhagic or thrombotic side effects of other drugs (e.g. oral contraceptives). The thrombogram thus is a promising new approach to clinical management of bleeding and thrombotic disease as well as a tool in drug research and epidemiology. Our experience at this moment is insufficient, however, to already clearly define its limits.