1. To reveal the mechanism responsible for the increase in blood pressure (BP) response to high salt intake in salt-sensitive essential hypertensives, pressor responses to angiotensin II and norepinephrine on high and low salt diet, influence of high salt intake on calcium metabolism and insulin sensitivity were studied in essential hypertensive and in normotensive subjects with or without family history of hypertension. 2. Pressor responses to angiotensin II and norepinephrine were significantly increased in salt-sensitive essential hypertensives irrespective of high or low salt diet. 3. In normotensive subjects with positive family history, high salt diet elevated BP in association with an increase in urinary calcium excretion. This observation, however, was not shared by the normotensive subjects with negative family history of hypertension. In the normotensive subjects with positive family history of hypertension, the cytosolic calcium concentration in platelets was significantly higher than in those with negative family history. A significant correlation between the cytosolic calcium concentration and elevation of BP was also observed. 4. In normotensive subjects with family history of hypertension, insulin sensitivity was decreased and correlated negatively with the cytosolic calcium concentration. 5. These results suggest that in salt-sensitive essential hypertensives increased pressor responses to angiotensin and norepinephrine and elevation of BP as well as insulin resistance may result from inherited abnormalities of intracellular calcium metabolism.