Several investigators recently have reported that the administration of digitalis to animals causes a decrease in the clotting time of blood. Tanaka1 noted an acceleration of coagulation when strophanthin was given intravenously to rabbits; the drug in vitro was without effect. During the past year Macht2 in a group of experiments concerning the influence of heparin on the toxicity of digitaloids discovered that administration of heparin to cats prior to intravenous injection of solutions of ouabain and digitalis significantly lowered the toxicity of these drugs. In addition, he found that the various digitaloids when added to shed blood in vitro hastened coagulation. Shortly thereafter Werch3 pointed out that a significant reduction of the coagulation time resulted when digitalis was given intravenously to rabbits. The present study was carried out in order to determine whether therapeutic doses of digitalis would similarly affect the coagulation time in man.