The rapid turnover rate of plasma proteins involved in coagulation has been offered as evidence for a process of continuous subclinical in vivo coagulation. By administration of a continuous intravenous drip of heparin to four normal subjects, no significant change was demonstrated in the rate of disappearance of proconvertin and prothrombin from the circulation after blocking the production of these factors by the administration of a large dose of Warfarin sodium. This evidence does not disprove the existence of continuous coagulation, but the rapid turnover rate of coagulation factors would not appear to be sound evidence for such a process. Submitted on March 11, 1960