This study aimed to elucidate the effects of intravenously infused magnesium on renal calcium and sodium metabolism in patients with essential hypertension. Mean arterial pressure (MAP), heart rate (HR), urine volume (UV), endogenous creatinine clearance (Ccr), urinary excretion of calcium (UCaV) and sodium (UNaV), fractional excretion of calcium (FECa) and sodium (FENa), plasma ionized calcium (pCa2+) and parathyroid hormone(PTH) were measured before and after intravenous infusion of 10% magnesium sulfate (initial dose: Mg 13.5mg/m2.BSA/15 min.: maintenance dose: Mg 2.7mg/m2.BSA/105min) in 6 normotensive subjects (NT) and 13 mild-to-moderate essential hypertensives (EHT). After the magnesium infusion, significant increases of UV, UCaV, UNaV, FECa and FENa, and a significant decrease of PTH were observed in both NT and EHT while MAP and HR did not change in either group. PCa2+ significantly decreased and Ccr tended to increase only in EHT. Although no significant difference was found in the change in Ccr (delta Ccr) or PTH (delta PTH) between NT and EHT, the changes of UCaV (delta UCaV), UNaV (delta UNaV), FECa (delta FECa) and FENa (delta FENa) were greater in EHT than each in NT. A positive correlation was found between delta UCaV and delta FECa, as well as delta UCaV and delta Ccr, but the former was more remarkable in both groups. In addition, delta UCaV was positively correlated with delta FENa in EHT, but not in NT. No significant relationship was observed between delta UCaV and delta PTH in either group.(ABSTRACT TRUNCATED AT 250 WORDS)