As a probe of the noradrenergic system in depression, single oral doses of the tricyclic antidepressant desipramine (100 mg) and placebo were administered to unipolar and bipolar depressed patients and healthy volunteers. Plasma concentrations of norepinephrine (NE) were determined 2-3 hours after dosing, with subjects in supine and upright positions. On the placebo day plasma NE was low in a subset of bipolar patients; both groups of depressives demonstrated an exaggerated increase in plasma NE upon standing. After desipramine dosing, the orthostatic procedure resulted in even greater relative increments in plasma NE in both patient groups, with no change in volunteers. These data are consistent with noradrenergic dysregulation in depression.