A positive relationship between hypoproteinemia and susceptibility to shock has been predicated on the observation that the hypoproteinemic animal is prone to have a decreased plasma volume1 and that it is generally incapable of replacing any further loss in plasma protein rapidly because the stores of labile protein are largely exhausted. Little if any direct experimental evidence on this point has been reported, and yet the importance of this relationship is so practical, from the standpoint of both war surgery and civilian surgery, that the following experiments were undertaken with a view to establishing not only whether such a relationship does exist but whether it is quantitatively of sufficient importance to justify greater care in avoiding hypoproteinemia in persons who are likely to be exposed to shock-producing injuries. METHOD The experiments were carried out on mongrel dogs weighing 8 to 13 Kg. Hypoproteinemia was produced by repeated plasmaphereses in