A group of 27 patients with panic disorder with or without agoraphobia were compared with 10 control subjects before stress exposure. No statistically significant differences between patients and controls were found for the cardiovascular parameters. Skin conductance level and skin conductance reaction were significantly higher in the patient group. They also showed higher self-ratings in behavioural symptoms associated with anxiety. There were statistically significant higher venous plasma levels of norepinephrine in patients than in controls, although the epinephrine levels were similar. The number of binding sites of alpha 2-receptors and the affinity of 3H-yohimbine to the alpha 2-receptors on intact thrombocytes was statistically significantly lower in patients compared to controls. Significant differences between the gender groups of patients and controls were found for electrodermal activity and epinephrine levels. These data add further evidence to an overshooting activation of the noradrenergic pathway in patients with panic disorder, possibly based on a dysregulation of alpha 2-receptor.