The heptadecapeptide ACTH 1-17 is the analogue of corticotropin with beta-alanine in position 1, lysine instead of 17-arginine and a basic amide instead of 18 arginine-amide. These modifications give enhanced biological activity and longer duration of the action. Several researchers investigated the acute effect of the analogue after administration at different time points along the 24 h cycle, and discovered that glucocorticoid and mineralocorticoid responses are dissociated in terms of doses and timing. Cortisol and urinary 17 OH-CS rise more after morning injections whereas for aldosterone the maximum effect was noted at 14(00). The most interesting finding that concerns ACTH 1-17 is the chronizing effect. ACTH 1-17 can be a chronizer because its administration resets, for instance, the toleration to antimitotic drugs, to a more convenient time. At clinical level, a group of researchers studied, in some case correctly from a chronobiological point of view, the effect of the ACTH 1-17 on patients and on healthy subjects. It is useful to remember the concept of hierarchies of rhythms: each different periodic function is regulated or, better, intermodulated by a network of other periodic variables of the same organ or of other organs and systems. So the necessity of large samplings to evidentiate periodic phenomena, and the utility of investigating pertinent marker rhythms significantly correlated with those to be studied are evident. Autorhythmometry and automatic monitoring can help very much on this purpose.