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).