In the present study twelve chronic hemodialysis (HD) patients will be included. Exclusion criteria are use of acetylsalicylic acid and/warfarin, clinical signs of infection and disseminated malignant disease. For each patient four HD sessions will be investigated; alternating with use of the pre-heparin-coated filter or the conventional filter. Dalteparin is reduced to 50% of the conventional dose and is given as one single bolus dose at start of HD.