Adrenocortical function and plasma growth hormone pattern were investigated in 15 patients with chronic obstructive lung disease, in a period of acute respiratory failure and again after recovery. During the acute period, secretion rate and plasma concentrations of cortisol were markedly enhanced; urinary excretion of cortisol metabolites was only slightly increased, suggesting an alteration of the catabolism of cortisol under these conditions; adrenocortical sensitivity to corticotropin and capacity of maximal adrenal secretion were normal. The increase of cortisol secretion was probably due to hypoxemia and/or hypercapnia acting through the hypothalamo-pituitary axis. During the chronic phase of respiratory insufficiency, adrenocortical secretion and responsiveness were within the normal range. Finally, respiratory failure did not stimulate the secretion of growth hormone.