Although the existence of salt sensitivity in essential hypertensives has been well known, the precise mechanism(s) has not yet been elucidated. The aim of this study was to clarify the relation between the responses in blood pressure, extra- and intracellular cations and calcium-regulating hormones to oral NaCl loading in essential hypertensives. After oral NaCl loading, mean blood pressure, urinary excretions of calcium and magnesium, and PLT[Ca2+]i were significantly increased. [Ca2+]o and E[Mg]i were decreased. The changes (delta) in mean blood pressure by NaCl loading positively correlated with delta PLT[Ca2+]i and delta PTH, and negatively with delta[Ca2+]o and delta E[Mg]i. Delta PLT[Ca2+]i positively correlated with delta PTH and negatively with delta[Ca2+]o and delta E[Mg]i. From these results, the blood pressure response to oral NaCl loading is associated with the alternation of [Ca2+]i metabolism in which the changes in magnesium metabolism and calcium-regulating hormones may be involved.