THE POSSIBILITY that abnormalities in the sympathetic nervous system (SNS) cause panic disorder has been a central concern for well over a century. As early as 1871, DaCosta1 attributed the cause of "irritable heart" in soldiers to "hyperaesthesia of the cardiac nerve centers" (the description is similar to panic disorder). Important new data on this problem is now provided by Wilkinson et al2 who used infusion of radiolabeled epinephrine and norepinephrine with arterial catheterization and coronary sinus sampling and microneurography to assess the SNS in patients with panic disorder and healthy controls. No evidence of heightened SNS tone at rest was found in these patients. However, a marked increase in total body epinephrine-appearance rate (ie, spillover rate) and a smaller increase in the norepinephrine-appearance rate was seen during a spontaneous panic attack in the 3 patients who had one while measurements were being made. Increased appearance of both epinephrine and norepinephrine during a "stressful" mental arithmetic task was not different in the patients and controls.