Maternal magnesium requirements increase during pregnancy because of the synthesis of new tissue - both fetal and maternal. Magnesium takes part in almost 300 enzymatic reactions in the human body and regulates membrane permeability and protein bio­synthesis by promoting initiation and dissociation factors. The absorption velocity of magnesium differs from one tissue to another in animal experiments. It is highest in the liver, kidney, heart and is low in skeletal muscle, the brain and erythrocytes. It obeys and follows the Michaelis-Menten Kinetic law. 15 mmol of magnesium is consumed daily depending on the types of food takenin. The main sources of magnesium are vegetables and meats. Many Nigerian women are not able to afford enough of these. The amount of magnesium reabsorbed depends on the magnesium intake and not on magnesium needed which is about 10-40% of the intake. In this study, we examined the short-term effect of magnesium asphat HCL (614. 18 mgMG), magnesium diasporal (magnesium citrate 610 mg+ magnesium laevalitat 30 mg= 100 mg magnesium= 8.2 mval), ferrous gluconate (300 mg) plus folic acid and chemiron, a new combination hematinic agent (ferrous fumarate 300 mg, folic acid 5 mg, vitamin B12 10 mg, vitamin C 25 mg, magnesium sulfate 0.3 mg and zinc sulfate 0.3 mg) on plasma magnesium concentration during early pregnancy in Nigerian women. Significant increases of plasma magnesium concentrations were found in these groups (magnesium asphat HCL, 0.83 ± 0.12 to 0.96 ± 0.14 mmol/1,magnesium diasporal 0.843± 0.14 to 0.891 ± 0.14 mmol/1 and chemiron 0.848 ± to 0.866 ± 0.16 mmol/1 after five days. The ferrous gluconate and folic acid treated group showed no significant changes. This study shows that a chemiron supple­ment leads to increased magnesium plasma levels whereas ferrous gluconate and folic acid do not. These results suggest that the low level of magnesium is a normal physiological adjustment of pregnancy and that iron supplementation does not influence this unless magnesium salt is given.