The authors assessed in a group of 10 healthy volunteers the Mg content of serum, in erythrocytes (Er) and lymphocytes (Ly) before infusion and during three hours after infusion of 400 ml 10% glucose without added Mg and with addition of 10 ml 20% MgSO4 (magnesium sulphate, Spofa). It was revealed that glucose infusion without Mg reduces significantly serum magnesium as well as Mg in lymphocytes and the reduced values persist for at east three hours after termination of the infusion. In 3 of 10 volunteers the values dropped beneath the lower range of reference values; two of these three volunteers developed also clinical manifestations of Mg deficiency. Mg in Er was not affected by the glucose infusion. The glucose infusion with Mg raised significantly the serum Mg and Mg in Ly; Mg in Er did not change. Based on the submitted results the authors recommend prevention of Mg deficiency induced by glucose infusion by Mg supplementation, in particular in patients with cardiovascular diseases.