Patients will begin the study using their currently prescribed heparin doses - both bolus and constant infusion - for three treatments to establish a baseline and provide information on inter-treatment variability in dialyzer clotting. Subsequently, the bolus and infusion rates will be titrated either upward or downward based on the Robbins-Monro process and an evaluation of dialyzer clotting during the preceding treatment. Heparin doses will be adjusted for a total of 30 dialyses.

The objective is to titrate each patient's heparin dose to the level that achieves adequate anticoagulation for that patient as assessed by the change in blood compartment volume of the dialyzer from pre- to post-dialysis. The strategy that will be used is the Robbins-Monro stochastic approximation algorithm.

Visual assessment of the dialyzer,measurement of ionic dialysance and ionic Kt/V.