A totally heparin grafted dialysis system shows great promise in the treatment of chronic uremia associated with bleeding risk. 2. Long-term treatment of chronic uremia with this system has to await: a) Further studies of the chronic toxicity of CPC. b) Evaluation of performance which may be achieved by using a more homogeneous heparin with higher bioactivity. 3. Detailed studies of platelet factor 4 release with subsequent heparin neutralization to determine the importance of this variable in its effect on system performance.