The hypothalamic-hypophysial control of basal adrenal cortical function was investigated in three avian species, by means of adenohypophysectomy (HE) and pituitary autografting (AG). HE led to a marked decrease of the plasma corticosterone content: (36 to 43 % of controls in ducks, 54% in pigeons, 46% in quail), and of adrenal corticosterone (16 % in ducks and pigeons, 30 % in quail), while the adrenal aldosterone content remained unaltered. The biological half-life (T½) of 3H-corticosterone showed a twofold increase, and the metabolic clearance rate (MCR) of the hormone was reduced to 60 % of the control values, in the duck. These results are discussed in the light of a possible extra-hypophysial adrenocorticotropic control. Provided the post-operative time lapse was sufficient to offer the grafted ectopic pituitary the possibility of functional resumption, the plasma corticosterone level was maintained at 80 % of the control values in ducks, 77 % in pigeons, and 90 % in quail; the T½and MCR of 3H-corticosterone were also found to be restored. However, the adrenal corticosterone content was low (30 % of the control values in ducks and pigeons, 75% in quail); the adrenal aldosterone level was normal. The relative importance of CRF is discusse