The concentration of noradrenaline, adrenaline, corticosteroids and ascorbic acid in the adrenal glands of intact cats was studied after administration of adrenocorticotrophin (ACTH), insulin or glucagon. The animals were injected intraperitoneally with either hormone and killed 1or 3 h later. Significant increases of corticosteroids were found in all experiments after ACTH or insulin but a significant decrease was observed 1 h after glucagon administration. Adrenal ascorbic acid decreased significantly 1 and 3 h after ACTH but only 1 h after treatment with insulin, and glucagon, or when both hormones were given simultaneously. A significant increase in the content of adrenaline was found 3 h after single ACTH injection in the absence of significant variation of the levels of noradrenaline in the adrenal gland. Significant decreases of noradrenaline and adrenaline were found 1 and 3 h after insulin as well as 1 h after glucagon administration. A decrease of catecholamines was also obtained following the simultaneous administration of insulin and glucagon. These findings suggest that the decrease in adrenaline may be secondary to the significant decrease in adrenal noradrenaline; they also indicate that in the intact cat the glucocorticoid levels may regulate the methylation of noradrenaline without being, however, the only factor involved in the control of adrenaline production by the adrenal gland.