Abstract. According to Selye (1907 – 1982) stress is defined as “nonspecific response of the body to any demand”, eliciting the General Adaptation Syndrome, which is characterized by three stages: alarm reaction – adaptation – exhaustion. Hence, a given stressor, e.g., forced muscular work, can be harmful on acute or prolonged exposure (“distress”) or beneficial at increased level of resistance (“eustress”). Magnesium (Mg) acts as physiological Ca 2+ and NMDA receptor antagonist, stimulates GABA A receptors, inhibits glutamate release from presynaptic neurons, and leads to synaptic strengthening. In cats with chronically implanted electrodes, oral Mg caused electrophysiological alterations characteristic for tranquillizing effects. Accordingly, plentiful Mg supply attenuates the release of stress hormones in humans and protects livestock against diverse stressors. Positive effects on mood, sleep, depression, and affective disorders have also been reported. On the other hand, Mg deficiency sensitizes against various stressors, e.g., noise stress, cardiovascular diseases, functional disorders in children and adults, and ethanol withdrawal. Mg deficiency also plays a key pathogenic role in the development of diabetes, hypertension, and osteoporosis. Consequently, plentiful Mg supply is recommended for coping with distress either utilizing its pharmacological or its (patho-)physiological effects.