Minimal dose heparinization inhibiting clotting factor IXa, Xa, XIa, as monitored by the activated partial thromboplastin time, was compared with conventional intermittent, continuous and regional heparinization during hemodialysis treatment. Blood loss in coil dialyzers was the same. Heparin dosage was reduced markedly. Protamine sulfate and infusion equipment were not required. No bleeding problems were encountered in high-risk patients.