Basal serum cortisol, growth hormone, prolactin and immunoreactive (IR) plasma beta-endorphin levels were measured in 31 depressed patients (14 endogenous, 17 nonendogenous) undergoing the dexamethasone suppression test. The endogenously depressed patients had significantly higher (22.55 +/- 1.34 micrograms/dl) predexamethasone cortisol levels than the nonendogenous patients (16.34 +/- 1.93 micrograms/dl). The mean serum prolactin and growth hormone values of these two groups were not significantly different, while plasma IR-beta-endorphin levels of the endogenous group (40.11 +/- 3.57 pg/ml) were significantly lower than those of the nonendogenous group (120.33 +/- 27.98 pg/ml). Neither group showed a significant correlation between plasma IR-beta-endorphin and serum cortisol values. These results indicate that measurement of predexamethasone serum cortisol values and plasma IR-beta-endorphin could be valuable laboratory tests in the diagnosis of depression.