It is well established that the adrenocorticotropic hormone (ACTH) stimulates the synthesis and release of cortisol from the adrenal cortex, but the role of ACTH in the physiological regulation of basal cortisol secretion has received surprisingly little study. The authors studied the nocturnal and early morning secretory pulses of cortisol and ACTH in normal subjects. A pulse detection algorithm was developed. The relationship between ACTH and cortisol pulses in terms of temporal and proportional relationship is described. Pulse concomitance for ACTH with cortisol was 47% and for cortisol with ACTH pulses it was 60%. The first description of the relationship between concomitant ACTH and cortisol pulse magnitudes in humans is presented. A highly significant linear relationship between the magnitudes of ACTH and cortisol pulses is shown. Putative reasons for dissociated pulses and the potential implication of these findings are discussed.