There is current controversy over the mechanisms underlying hypothalamic-pituitary-adrenal (HPA) axis hyperactivity in depression. Pro-gamma-melanocyte-stimulating hormone (MSH), a portion of the N-terminal region of pro-opiomelanocortin, has been shown to act synergistically with adrenocorticotropic hormone (ACTH) in stimulating corticosteroid secretion both in vitro and in vivo. Pro-gamma-MSH and ACTH plasma levels were measured in 30 drug-free male patients with a DSM-IIIR major depressive disorder and 21 healthy controls. The baseline levels were similar in the two groups. After single-dose metyrapone stimulation, both hormones increased, but pro-gamma-MSH was significantly higher in control subjects than in depressives. After overnight 1-mg dexamethasone, ACTH was significantly less suppressed in depressives than controls. These results suggest that HPA axis dysregulation in depression may involve peptides other than ACTH and be more complex than previously reported.