Plasma cortisol levels of 28 hospitalized patients meeting Research Diagnostic Criteria for major or nonmajor (minor or intermittent) depression were significantly higher than those of eight normal subjects. In contrast, plasma beta-endorphin immunoreactivity was significantly lower in patients with nonmajor depression than in those with major depression or in normal subjects. A low ratio of plasma beta-endorphin to cortisol immunoreactivity was found to characterize patients in both groups. Through the use of only this ratio, a post-hoc analysis identified 25 depressed patients and seven controls. These findings have implications for psychiatric diagnosis and the involvement of the endogenous opioid system in the pathogenesis of depression.