Plasma ionized calcium, platelet cytosolic calcium (using the fura-2 method in gel-filtered platelets), parathyroid hormone (both the intact hormone and a midmolecule portion), calcitriol, and calcidiol were measured in 19 untreated male patients with essential hypertension and 19 age-matched normotensive male research subjects. Mean levels of platelet cytosolic calcium, parathyroid hormone, calcitriol, and calcidiol were all significantly higher, whereas plasma ionized calcium was significantly lower, in the hypertensive group compared with the normotensive group. Both platelet cytosolic calcium and intact parathyroid hormone were positively correlated with mean arterial pressure (r = 0.58, p less than 0.001; r = 0.54, p less than 0.001, respectively), whereas plasma ionized calcium was inversely correlated with mean arterial pressure (r = -0.60, p less than 0.001) in the combined group of all study subjects. All three of these correlations were significant in the hypertensive group alone but not in the normotensive group alone. When analyzed with plasma ionized calcium, body mass index, serum calcitriol, and calcidiol in a multivariable regression model, the significance of the partial regressions of platelet cytosolic calcium and parathyroid hormone with mean arterial pressure persisted. Intact parathyroid hormone was positively correlated to platelet cytosolic calcium (r = 0.43, p less than 0.01) and plasma ionized calcium was inversely correlated to platelet cytosolic calcium (r = -0.44, p less than 0.01). These results confirm previous reports of disturbances of calcium metabolism in essential hypertension and suggest that the elevated platelet cytosolic calcium observed in essential hypertension may be linked to one or more of these alterations of calcium metabolism.