Both stress-system activation and melancholic depression are characterized by fear, constricted affect, stereotyped thinking, and similar changes in autonomic and neuroendocrine function. Because norepinephrine (NE) and corticotropin-releasing hormone (CRH) can produce these physiological and behavioral changes, we measured the cerebrospinal fluid (CSF) levels each hour for 30 consecutive hours in controls and in patients with melancholic depression. Plasma adrenocorticotropic hormone (ACTH) and cortisol levels were obtained every 30 min. Depressed patients had significantly higher CSF NE and plasma cortisol levels that were increased around the clock. Diurnal variations in CSF NE and plasma cortisol levels were virtually superimposable and positively correlated with each other in both patients and controls. Despite their hypercortisolism, depressed patients had normal levels of plasma ACTH and CSF CRH. However, plasma ACTH and CSF CRH levels in depressed patients were inappropriately high, considering the degree of their hypercortisolism. In contrast to the significant negative correlation between plasma cortisol and CSF CRH levels seen in controls, patients with depression showed no statistical relationship between these parameters. These data indicate that persistent stress-system dysfunction in melancholic depression is independent of the conscious stress of the disorder. These data also suggest mutually reinforcing bidirectional links between a central hypernoradrenergic state and the hyperfunctioning of specific central CRH pathways that each are driven and sustained by hypercortisolism. We postulate that ␣-noradrenergic blockade, CRH antagonists, and treatment with antiglucocorticoids may act at different loci, alone or in combination, in the treatment of major depression with melancholic features. M ajor depression is a complex disorder with an estimated lifetime prevalence of 15% in women and 8% in men (1). Depression is the main cause of suicide: Ϸ70% of all suicides are attributed to untreated depression. Studies in the United States suggest that, at any given time, Ϸ2-3% of the population is hospitalized or seriously impaired by affective illness. The World Health Organization has declared major depression as the single largest cause of morbidity for women and the leading cause of disability worldwide.The current standard diagnostic instrument for psychiatry, the Diagnostic and Statistical Manual of Mental Disorders, 4th Ed. (DSM-IV) (2), lists two subtypes of major depression, melancholic and atypical. The features of melancholic depression include insomnia (most often early morning awakening), loss of appetite, weight loss, inappropriate guilt, and lack of pleasure (anhedonia). The second major subtype is major depression with atypical features, characterized in part by hypersomnia, hyperphagia, lethargy, and fatigue. The subclassification of depression provides direction for the appropriate choice of antidepressant medication. Studies in identical twins show a significantly higher concordance for ...