A series of controlled prospective clinical trials with supporting laboratory investigations in the pathophysiology of thrombotic states and related conditions and the pharmacology of new antithrombotic and hemostatic drugs will be conducted. The principal clinical trials, which are already in progress, include: (1) Study of a hemodynamically optimized system for external pneumatic compression of the lower limbs to prevent venous thrombosis in patients undergoing neurosurgical operations. (2) Investigation of the effectiveness and safety of therapy of established venous or arterial thromboembolism with a heparin preparation of low molecular weight and high antithrombin affinity. (3) Trial of the prevention of venous thromboembolism in patients with fractures of the hip by administration of a heparin-like compound (Organon 10172). (4) Administration of DDAVP to improve hemostasis in patients undergoing cardiopulmonary bypass and exploration of the role of von Willebrand's factor in the hemostatic defect in such patients.