Employing the injection technic for venous distensibility determinations in intestinal loops of anesthetized dogs, an index to venomotor tone has been developed by measuring the volumes of blood required to produce specified changes in venous pressure. Application of this index in hemorrhage and shock experiments demonstrates a marked venomotor compensation to hemorrhage, and oscillations in venomotor tone correlating with the vasomotor waves in arterial blood pressure encountered in hemorrhagic hypotension. In the hypotension of shock, a serious deficiency in venomotor compensation develops, which should result in pooling of blood in the venous system and contribute significantly to the circulatory failure.