The hemorrhagic risk of an association of fractioned heparin (Fraxiparine) injected intravenously at the dose of 7500 AXaICU or of unfractionned heparin (UFH) injected intravenously at the usual dose used for a priming dose for hemodialysis (3750 +/- 1280 IU + 1000 IU after 2 hours of dialysis) to the subcutaneous administration of a thrombo-embolism preventive dose of Fraxiparine (7500 AXaICU) was evaluated on the modifications of the following hemostasis parameters: thrombin time, Activated Partial Thrombin Time (APTT), prothrombin time, anti Xa activity in 13 uremic patients on hemodialysis. The association of intravenous and subcutaneous Fraxiparine prevents efficiently the clotting of the extracorporeal circulation without inducing a detectable antithrombinic activity. In contrast, the association of I.V. UFH to subcutaneous Fraxiparine induces a significant increase of the thrombin time and of the APTT. This latter is exclusively explained by the activity of UFH. It is concluded that subcutaneous Fraxiparine at the thromboembolism preventive dose can be associated as well to I.V. Fraxiparine as to UFH without increasing the antithrombinic activity of the plasma.