Plasma factors have been implicated in causing increased calcium uptake and cytosolic (Ca++) in vascular tissue leading to hypertension. We compared the effect of plasma from hypertensive and normotensive subjects on rat aortic calcium uptake. Plasma from hypertensive subjects was fractionated and the fractions assessed for their activity on aortic calcium uptake. Aortic calcium uptake was significantly higher in plasma from hypertensives as compared to normotensives (p less than 0.05). There was a significant positive correlation between diastolic blood pressure and aortic calcium uptake (r = 0.645; p = 0.002). There was a significant positive correlation between percentage ideal body weight and aortic calcium uptake in normotensives and hypertensives (r = 0.522; p less than 0.05). The calcium uptake stimulatory activity in plasma of hypertensives was found in nonesterified fatty acid and cholesterol ester fractions.