A number of drugs can influence Mg metabolism and produce changes in serum Mg concentrations. These alterations must always be considered in the differential diagnosis of cases with Mg disturbances. Hypermagnesemia is seen, particularly after administration of Mg-containing drugs in renal insufficiency. Marked hypomagnesemia can be observed in a great number of patients, particularly in those treated with loop diuretics, osmotic substances and with antineoplastics, such as cisplatin.