Experiments were performed to study the effect of dietary sodium deficiency on the in vitro biosynthesis of corticosteroids from tritiated cholesterol by homogenates of whole adrenal glands and on the properties of rat adrenocortical cytochrome P-450. Adrenal homogenates of rats kept on a sodium deficient diet for 17 days converted 3 times more tritiated cholesterol to corticosterone, 15 times more to 18-hydroxycorticosterone, and 6 times more to aldosterone than did homogenates from rats kept on the control diet. While adrenocortical cytochrome P-450 content did not differ significantly in the glands of experimental animals from that of control animals, changes could be observed in the cytochrome P-450 – carbon monoxide association time constants (KCO).