[Problems posed by etiologic research on thrombotic conditions].

In venous thrombosis conditions, the biological etiological survey is, to day, absolutely necessary. In approximately 30 p. cent of the cases of recurring venous thrombosis, there is a deficit in Protein S, Protein C, antithrombin III, a plasminogen or fibrinogen abnormality and a lack of fibrinolysis. On the contrary, despite of the obvious role of platelets in arterial thrombosis, the biological survey is more difficult.