According to big clinical trails Mg 2+ deficiency plays a major role in health and promote development of different chronic diseases. It is necessary to cooperate clinical symptoms and results of objective methods (ECG, myography, bone densitometry, level of Mg 2+ in hole blood, erythrocytes, serum, saline, urine, nails, hair) in case of diagnosis Mg 2+ deficiency. It is desirable to analyze Mg2+ intake with food by standard questionnaires. To have the full picture of Mg 2+ deficiency it is necessary to define level of Mg2+ in different biosubstrates.