MAJOR SURGERY and hemorrhagic shock represent typical examples of body injuries in which adequate blood and fluid replacement may be vital for recovery. Although the metabolic effects of surgical trauma have been the subject of many studies over the last 20 years, posttraumatic changes in body water composition remain controversial. In fact, current disagreement exists over whether there is a change in extracellular water volume greater than that explained by losses from the vascular compartment.1-6 Shires and others7-10 have reported a large deficit in the interstitial fluid volume after major surgery and hemorrhagic shock. This observation has led to the infusion of large volumes of balanced salt solutions during and after surgery. On the other hand, excessive use of salt-containing solutions may be associated with serious side effects particularly in the elderly patient with cardiovascular, renal, or liver disease.11,12 It should be recognized that much of the