The purpose of this study is to investigate whether the dialysis filter AN69ST (Nephral 400 ST Dialysis Membrane) induces less clotting during hemodialysis than a conventional polysulphone filter. Our hypothesis is that the two filters induce the same degree of clotting.

Six consecutive hemodialysis (HD) sessions are evaluated per patient, altogether 10 - 12 stable HD patients (or at least 48 HD sessions altogether). During these six sessions, AN69ST and Fx8 are used on alternate days. Dalteparin is given intravenously as a single bolus dose at start of HD (50% of the conventional dose). Clinical clotting is evaluated visually each hour of HD after blood draining of the venous air trap: 1=no clot, 2=a fibrinous ring, 3=a clot <1 cm, 4=a clot >1 cm and 5=coagulated system (stop in HD).

Blood specimens are taken at start and after each hour of HD. Markers of coagulation (prothrombin 1+2) and of platelets (beta-thromboglobulin) are evaluated as well as anti FXa-activity.

The two filters are going to be compared statistically with respect to the degree of clinical clotting and of intravascular coagulation and platelets activation.

Inclusion Criteria:

• patient aged 18 years or more having been in chronic HD for at least 1 month
• dialysis time at least 4 hours 3 times per week
• blood flow at least 200 ml/min
• Fragmin dose unchanged the last week before study start
• Fragmin given intravenously as one single dose at HD start
• Haemoglobin >= 11.0 g/dL and stable +/- 20% the last week before study start
• erythropoietin and iron dose unchanged the last week before study start
• written and orally informed consent given by the patient

Exclusion Criteria:

• treatment with acetylsalicylic acid (ASA)
• use of Warfarin or another oral anticoagulant
• clinical signs of infection
• disseminated malignant disease