Gram for gram, dextrans are more potent blood volume expanders than are plasma proteins despite their similarity in molecular weight. When the oncotic pressures of the two types of commercially available dextrans were studied, dextrans exerted oncotic pressures that were two to eight times those exerted by comparable concentrations of plasma proteins. Other experiments demonstrated that the dextrans diminished interstitial fluid volume chiefly because they exert such elevated oncotic pressures. A clinical application of this work is found in the use of dextrans to treat hypovolemia. That is, in contrast to whole blood or plasma, dextran infusions require much more Ringer's lactate solution to restore the volume of interstitial fluid from the reduced level in hemorrhagic shock to normal levels.