As a consequence of chemotherapy and radiation therapy an increased rate of thromboembolic complications has been monitored in clinical studies. Spontaneous or therapy induced liberation of thromboplastins and thrombin has been shown to be the molecular mechanism. The increased liberation of thromboplastins by tumour cells has additional consequences: thrombin does not only act as enzyme of the haemostotic system, but is able to induce increased proliferation of tumour cells or, in higher concentrations, even apoptosis. Additionally, we could demonstrate that the preincubation of leucaemic cells (HL-60) with thrombin reduces the rate of apoptosis induced by the topoisomerase inhibitor idarubicin. The reduction of thrombin liberation in tumour patients by anticoagulation therefore might increase the effect of idarubicin to induce apoptosis. This combined effect of anticoagulation and chemotherapy on apoptosis has to be investigated in further clinical studies.