The application of lower body positive pressure with military antishock trousers (MAST) to dogs in a 45d` head-up tilt is known to increase cardiac output and blood pressure, and to maintain life. In the present study we used MAST in an attempt to improve the natriuretic response to saline loading in normal and edematous anesthetized dogs. Twelve normal dogs were saline-loaded (7% body weight) in the supine position with and without MAST 4 days apart. The increment in UNaV without MAST was 853.3±26µEq/min and averaged 870.4±33µEq/min with MAST (p>0.05). The dogs were then subjected to chronic thoracic caval constriction, and when ascitic were tested again. Now, the increment to acute volume loading was 87.6±12.1µEq/min without MAST and 92.8±8.8µEq/min with MAST (p>0.05). The application of lower body positive pressure (60-80 mm Hg legs; 40-60 mm Hg abdomen) is not effective in promoting a natriuretic response to acute volume loading in either normal or edematous dogs with profound disturbances to the Starling forces over an extensive vascular territory.