The therapeutic use of cortisol and its derivatives, anti-inflammatory corticoids, sets delicate problems to resolve because of cortisol's physiological roles and its circadian rhythms. Cortisol and the majority of its derivatives have desirable and undesirable effects that are time-related administration. The chronotherapeutic optimisation to increase desirable effects and safety of corticoids is shown in the treatment of adrenocortical failure, congenital adrenal hyperplasia and asthma. The knowledge of physiological and physiopathological rhythms of asthma permitted to realize oral treatment optimisation by using a number of corticoids. This knowledge puts in a prominent position the advantages of ciclesonide: a new inhaled corticoid. A chronobiologic approach could be used in a classic optimisation which involves a molecule modification and inhalation like routes of administration.