The compensatory cardiovascular response to hemorrhage includes a baroreceptor-induced activation of the sympathetic nervous system resulting in an attempt to reestablish MAP through peripheral vasoconstriction. If the hypotension is not reversed this compensatory vasoconstriction will progress to a loss of vascular tone known as vascular decompensation. The primary purpose of the present study was to compare the effectiveness of military antishock trousers (MAST) applied during the compensatory and decompensatory stages of hemorrhagic hypotension. MAST pressures of 30, 50, 70, and 90 mm Hg were applied during control, compensation, and decompensation. The results showed that MAST pressures up to 90 mm Hg were ineffective at raising mean arterial blood pressure (MAP) when applied to normotensive dogs; MAP increased 62% when MAST were applied during compensation as the result of a significant augmentation of cardiac output (stroke volume and heart rate) with no change in TPR; and a modest increase in MAP from 40 to 55 mm Hg occurred when MAST pressure was increased to 70 mm Hg during decompensation, which was accounted for entirely on the basis of an increased total peripheral resistance with no significant change in CO.