Aldosterone, renin activity (RA), cortisol, corticosterone, growth hormone (GH), Na and K in the plasma of 4 normal, Na-restricted subjects were measured half-hourly over a 24–26-hr period. Production of the hormones is episodic. With onset of sleep, aldosterone production rises consistently; during the awake hours, frequency, timing and magnitude of its secretory episodes are variable. The pattern of RA is essentially identical to that of plasma aldosterone. Plasma Na and K show no consistent intradiem pattern; their changes are usually not significant. Near the end of sleep a rise in cortisol production, preceded by minimum activity, occurs consistently; secretory bursts are variable in number, timing, and magnitude during the awake time. The corticosterone pattern is the same as that of cortisol. GH peaks near the onset of sleep; variable activity occurs during the awake hours. One of the subjects, on oral contraceptives, shows similar but magnified hormonal patterns. Aldosterone correlates best with RA; it correlates poorly with cortisol. Corticosterone and cortisol are highly correlated. The sleep-related peaks of aldosterone and that of GH may be dissociated. These data in the Na-depleted human subjects are consistent with the following concepts: a) the renin–angiotensin system is the main regulator of aldosterone production; b) corticosterone and cortisol are under the same control mechanism. Furthermore, the occurrence of unpredictable and apparently spontaneous peaks in plasma aldosterone and RA during the late AM hours may interfere with clinícal tests of aldosterone and RA responsiveness to stimuli (like upright posture, diuretics, etc.) carried out under the conditions of this study.