SummaryHaemodynamic parameters and vascular reactivity to norepinephrine were determined in 24 borderline hypertensive patients in comparaison with 12 normal subjects. Borderline hypertensives had high values of blood pressure (P<0.001), cardiac index (P<0.01) and heart rate (P<0.05) and normal values of total peripheral resistance. The pressor dose of norepinephrine was significantly increased (P<0.001) and was directly correlated with the cardiac output (P<0.001). This result was not observed with the angiotensin and isoproterenol and could suggest the role of the adrenergic system in borderline hypertension.