Using a new technique for determining transmucosal electrical potential difference (p.d.) and short-circuit current (Isc.) in the rat small intestine in vivo it would appear that aldosterone had no direct effect on these parameters of intestinal activity. However, adrenalectomy decreased the Isc. while after adrenalectomy aldosterone and cortisol (hydrocortisone) restored the lowered independent and probably also the lowered dependent (hexose) Isc.