The hypothalamic-pituitary-adrenal (HPA) axis is dysregulated in many patients with depression, probably at all levels of the axis. To determine if HPA dysregulation is associated with severity of depression, we studied a group of 66 patients with major depressive disorder. Each patient underwent a pretreatment Dexamethasone Suppression Test, with plasma postdexamethasone cortisol determination at 8:00 AM, 4:00 PM, and 11:00 PM. All three postdexamethasone cortisol levels were significantly correlated with the Hamilton Rating Scale for Depression (HRSD) scores. We also examined the "profile" measures of mean, maximum, and minimum of the three cortisol values; again, all three were significantly correlated with HRSD scores. To evaluate associations between clinical severity and HPA dysregulation at the pituitary level, we studied a second group of 44 patients with major depressive disorder. Each had postdexamethasone cortisol determinations at 4:00 PM and 11:00 PM as well as pre- and postdexamethasone β-endorphin determinations at 4:00 PM. The cortisol data from this group followed the same pattern as in the first sample, and there was a significant relationship between HRSD score and degree of β-endorphin nonsuppression as well. These results suggest that severity of depression is one of the determinants of dysregulation at both adrenal and pituitary levels of the HPA axis, accounting for 10%-20% of the observed variance. © 1987.