Asthma is a chronic, inflammatory disorder of the airways leading to airflow limitation. Its worldwide rise, mainly in developed countries, is a matter of concern. Nocturnal asthma (NA) frequently occurs and concerns two thirds of asthmatics. But, it remains controversial whether NA is a distinct entity or is a manifestation of more severe asthma. Generally, it is considered as an exacerbation of the underlying pathology. The pathological mechanisms most likely involve endogenous circadian rhythms with pathological consequences on both respiratory inflammation and hyperresponsiveness. A decrease in blood and tissue magnesium levels is frequently reported in asthma and often testifies to a true magnesium depletion. The link with magnesium status and chronobiology are well established. The quality of magnesium status directly influences the Biological Clock (BC) function, represented by the suprachiasmatic nuclei and the pineal gland. Conversely, BC dysrythmias influence the magnesium status. Two types of magnesium deficits must be clearly distinguished: deficiency corresponding to an insufficient intake which can be corrected through mere nutritional Mg supplementation and depletion due to a dysregulation of the magnesium status which cannot be corrected through nutritional supplementation only, but requires the more or less specific correction of the dysregulation mechanisms. Both in clinical and in animal experiments, the dysregulation mechanisms of magnesium depletion associate a reduced magnesium intake with various types of stress including biological clock dysrhythmias. The differenciation between Mg depletion forms with hyperfunction of BC (HBC) and forms with hypofunction of BC (hBC) is seminal and the main biological marker is melatonin (MT) production alteration. We hypothesize that magnesium depletion with HBC or hBC may be involved in chronopathological forms of asthma. Nocturnal asthma would be linked to HBC, represented by an increase in MT levels. The corresponding clinical forms associate diverse expressions of nervous hypoexcitability such as depression, cluster headaches, dyssomnia, mainly advanced sleep phase syndrome, some clinical forms of chronic fatigue syndrome and of fibromyalgia. The main comorbidities are depression and/or asthenia. They take place during the night or the "bad" seasons (autumn and winter) when sunshine is at a minimum. The corresponding chronopathological therapy relies on bright light phototherapy sometimes with additional psychoanaleptics. Conversely, asthma forms linked to hBC are less frequently studied as a whole and present a decrease in MT levels. They associate various signs of nervous hyperexcitability such as anxiety, diurnal cephalalgia (mainly migraine), dyssomnia, mainly delayed sleep phase syndrome, and some clinical forms of chronic fatigue syndrome and of fibromyalgia. The treatment relies on diverse forms of "darkness therapy", possibly with the help of some psycholeptics. Finally, the treatment of asthma involves the maintenance of a standard dosing schedule of anti-asthma drugs, a balanced magnesium intake and the appropriate treatment of the chronopathological disorders.