Abstract： Objective To assess the relationships between plasma and intracellular Ca2+, Mg2+ and blood cell membrane adenosine triphosphatase (ATPase) activity in normotensive and hypertensive subjects.Methods Plasma and intracellular Ca2+ , Mg2+ were measured with atomic absorption spectrophotometry, and red blood cell membrane Na+ -K+ ATPase and Ca2+ -ATPase activities were determined with colorimetric method in 55 patients with essential hypertension and 32 normotensive controls.Results The results showed that the hypertensive group consistently demonstrated a significant decreased activity of ATPase studied, with significantly lower plasma Ca2+ and higher cytosolic Ca2+ levels when compared with those in normotensive group (P<0.01 or P<0.05, respectively). No significant differences were found in either plasma Mg2+ or intracellular Mg2+ level between the two groups. Conclusions This study suggests that patients with essential hypertension have widespread depression of cell membrane Na+ -K+ -ATPase and Ca2+ -ATPase activities with plasma Ca2+ depletion and cytosolic Ca2+ overload, which may reflect an underlying membrane abnormality in essential hypertension. The celluar abnormalities may be related to the defective transport mechanisms that in turn may be aggravated by plasma Ca2+ depletion.