Daily profiles of plasma 18-hydroxy-11-deoxycorticosterone (18-OH-DOC) were studied in four normal supine men on a normal sodium intake. Blood was taken every hour from 01.00 to 24.00 hours. Plasma cortisol (F) and aldosterone (A) were determined hourly for comparative studies. 18-OH-DOC fluctuated considerably during the 24 h period of investigation, the highest values being found during the early morning hours in synchrony with F. The episodic secretions of 18-OH-DOC were also significantly correlated with those of A, which in turn paralleled those of F. We conclude that ACTH, plays a definite role in the regulation of 18-OH-DOC in normal supine men on a normal sodium diet.