The hypothalamus-pituitary-adrenal axis of heroin addicts was investigated by evaluating plasma cortisol levels throughout the day in 37 heroin abusers (HA), 17 of whom showed detectable morphine levels, indicating heroin administration in the previous hours and in 12 controls. All HA showed lower cortisol levels in basal condition (100.7 +/- 61.7 ng/ml, M +/- S.D.) compared to the control group (159.7 +/- 40.6, P less than 0.05). Moreover all HA (65.1 +/- 28.9%), and in particular those taking heroin during the study (39.1 +/- 41.4%), show a reduced cortisol decrease in the evening, which was significantly lower than in controls (85.3 +/- 10.1%; P less than 0.01). As far as the acute effects of opiates are concerned morphine (0.1 mg/kg) significantly reduced plasma cortisol levels within 60 min in a group of 8 healthy subjects. The same pattern was displayed by only 3/8 HA whose morphine levels were higher than 1 ng/ml, i.e. in those reaching the highest plasma morphine concentrations. These data indicate that chronic opiate abuse leads to a hypoadrenalism which could be the result of morphine-induced changes at the hypothalamic level.