Injection of 250μg 6 hydroxydopamine (6 OHDA) into the lateral ventricle of adult male and female rate resulted 1 wk later in: a lowered brain content of noradrenaline to 20% and dopamine to 40-50% that of control levels but no change in brain serotonin content; a slight reduction in male and no change in female body weight; no change in adrenal weight; minor or no changes in diurnal pituitary adrenal periodicity or in the responsiveness of this system to ether stress, laparotomy or exposure to a strange environment and handling. Dexamethasone blockade of the diurnal rise in adrenocortical activity was also unchanged. Intracerebral administration of 200 μg 6 OHDA to newborn male and female rats in 3 sequential doses of 40, 60 and 100 μg, resulted at 12 wk of age in: a lowered brain content of noradrenaline and dopamine to 10% that of control levels but no change in brain serotonin; a 30% decrease in body weight; no change in adrenal weight; minor or no changes in pituitary adrenal periodicity nor in the responsiveness to ether stress and exposure to a strange environment and handling. When minor changes after 6 OHDA treatment of adult or neonatal rats were found, they always pointed to a stimulatory function of brain catecholamines in pituitary adrenal activity. It is concluded however that a severe and chronic depletion of brain catecholaminergic systems has no important consequences for the normal functioning of the pituitary adrenal system.