This study examined the impact of enflurane (3%) on the hemodynamic and humoral defense mechanisms in a canine model of hemorrhagic shock. In order to obtain reasonable reference values with confounding influences of anesthesia and recent surgical preparation, the dogs were chronically instrumented 8-10 days prior to the experiments enabling measurements in the conscious state. While arterial pressure, cardiac output, and the corresponding derivatives were recorded continuously, plasma catecholamines and plasma renin activity were determined intermittently. As anticipated, the conscious dogs were able to tolerate considerable more severe levels of hemorrhage than the dogs anesthetized with enflurane. This finding is associated with reciprocal responses of both the renin-angiotensin system and the sympathoadrenal system in the conscious and anesthetized states. While the sympathoadrenal system prevailed in the conscious dogs, the renin-angiotensin system predominated during enflurane anesthesia. Despite the augmented response of the renin-angiotensin system, the activation of this defense mechanism was not sufficiently powerful enough to prevent overall hemodynamic deterioration with hemorrhage in the animals anesthetized with enflurane.