Erythropoietin was within normal range and similar among the three groups. In patients with established essential hypertension, a close correlation was found between erythropoietin and systolic (r = 0.45, P<0.002) and diastolic (r = 0.51, P<0.001) ambulatory blood pressure. In contrast, ambulatory blood pressure was not correlated with erythropoietin in subjects with borderline hypertension. Total peripheral resistance (r = 0.41, P<0