In experiments with the anaesthetized and acutely adrenalectomized cat it has been shown that the endogenous corticosteroids, cortisol and corticosterone are eliminated at the unstimulated normal level at a rate proportional to the plasma concentration. Hepatectomy prolonged the half life by a factor of about two (from 35 ± 8.6 to 79 ± 22 min) and total abdominal evisceration abolished all true elimination. Determinations of the arteriovenous difference across the portal system gave results in accordance with these results. A few experiments suggested that the intestine is responsible for the main part of the extrahepatic elimination. In experiments with the perfused isolated hindquarter preparation it was impossible to demonstrate any elimination of corticosteroids in spite of electrical stimulation or the administration of large amounts of insulin.