The author presents an account of results of the magnesium loading test and its method, from a group of 50 patients with cardiovascular diseases. The magnesium loading test reveals shortage of bodily reserves of magnesium (mg) by calculating the percentage of Mg retention. In a group of examined subjects the author found a high percentage of Mg retention (on average 68%) which suggests an unequivocal deficiency of bodily Mg reserves in this group of patients. At the same time changes of serum concentrations and urinary excretion of other investigated minerals are discussed. As compared with other methods of assessment of Mg bodily reserves, the loading test is most suitable for clinical practice. In the discussion the author analyzes the assembled results and factors which lead to deficiency of bodily Mg reserves and deals with substitution treatment by Mg preparations.