The urinary excretion of catecholamine acid metabolites, vanylmandelic acid (VMA) and homovanillic acid (HVA), in adrenalectomized and hypophysectomized rats was determined. The two above manipulations resulted in markedly increased excretion of both VMA and HVA in 24-hour urine samples and demonstrated high statistical significance from control rats. The increases were more profound after adrenalectomy. The administration of 5 mg of hydrocortisone daily to adrenalectomized rats produced gradual declines in VMA excretion after 3rd, 6th and 10th. After the 10th injection of hydrocortisone, the VMA excretion in the adrenalectomized rats was statistically insignificant from control rats. The administration of 4 IU of ACTH or 5 mg of hydrocortisone to hypophysectomized rats also returned the increased excretion of VMA to normal level. The HVA excretion followed similar pattern as VMA. After hypophysectomy and adrenalectomy urinary HVA increased significantly from control rats. The daily administration of hydrocortisone or ACTH, respectively, to adrenalectomized or hypophysectomized rats produced marked declines in HVA excretion. The results suggest that adrenal glucocorticoids serve as an inhibitory factor for catecholamine metabolite formation in normal rats. The absence of glucocorticoids is followed by increased levels of VMA and HVA.