Vasodilatory septic shock is characterized by profound vasodilation of the peripheral circulation, relative refractoriness to catecholamines and a relative deficiency of the posterior pituitary hormone, vasopressin. Arginine vasopressin is effective in restoring vascular tone in vasodilatory septic shock and may be associated with decreased mortality in less severe septic shock as well as improved mortality and decreased renal failure in septic shock patients at risk for renal failure.