There is considerable evidence that the hemostatic system is involved in the growth and spread of malignant disease. There is an increased incidence of thromboembolic disease in patients with cancers and hemostatic abnormalities are extremely common in such patients. Antihemostatic agents have been successfully used to treat a variety of experimental tumors, and several clinical trials in humans have been initiated. Although metastasis is undoubtedly multifactorial, intravascular coagulation activation and peritumor fibrin deposition seem to be important. The mechanisms by which hemostatic activation facilitates the malignant process remain to be completely elucidated. Of central importance may be the presence on malignant cells of tissue factor and urokinase receptor. Recent studies have suggested that these proteins, and others, may be involved at several stages of metastasis, including the key event of neovascularization. Tissue factor, the principal initiator of coagulation, may have additional roles, outside of fibrin formation, that are central to the biology of some solid tumors.