Magnesium is an essential factor in many important enzymatic reactions, either as an integral part of a metalloenzyme or as an activator, and plays an important role in glycolysis, cellular respiration and transmembranous calcium transport. Magnesium is mainly regulated by the rate of renal magnesium excretion, which along with calcium is subject to the effects of parathyroid hormone. Increasing calcium reabsorption thus leads to competitive inhibition of magnesium absorption. Magnesium measurements are used in the diagnosis and treatment of hypomagnesemia (abnormally low) and hypermagnesemia (abnormally high). The best-defined manifestation of magnesium deficiency is impairment of neuromuscular function e.g. hyperirritability, tetany, convulsions, and electrocardiographic changes. Hypomagnesemia is observed in cases of diabetes, chronic alcoholism, forced diuresis, hyperthyroidism, hypoparathyroidism, hypocalcemia, malabsorption and acute pancreatitis. Increased serum magnesium levels have been found in cases of renal failure, dehydration, severe diabetic acidosis and Addison’s Disease.