Platelet intracellular free calcium concentration was assessed by the quin-2 method in 38 patients with essential hypertension and in 35 normotensive subjects. The concentrations were found to be significantly higher in the hypertensive patients (p less than 0.05); however, there was a wide overlap between the values of both groups. In addition, we determined platelet intracellular free calcium in another model of increased blood pressure, the blood pressure elevation following administration of the synthetic mineralocorticoid fludrocortisone. Administration of 0.8 mg fludrocortisone per day to eight normotensive volunteers resulted in a pronounced increase in intracellular free calcium after the first week and a decrease toward control levels thereafter, while blood pressure remained elevated throughout the period of fludrocortisone administration. Our findings suggest that an increase in intracellular free calcium concentration is a transitory phenomenon and not directly related to the blood pressure elevation.