1. Previous investigations have demonstrated an impaired endothelium-dependent vasodilatation (EDV) in patients with hypertension. The present study aimed to investigate if an acute rise in blood pressure to hypertensive levels impairs EDV in otherwise normotensive subjects. 2. Twenty-seven young, healthy, normotensive subjects were studied. Eight of these underwent evaluation of EDV and endothelium-independent vasodilatation (EIDV) by means of forearm blood flow measurements during local intra-arterial infusions of methacholine (2 and 4 micrograms/min) and sodium nitroprusside (5 and 10 micrograms/min), before and after 1 h of sustained hypertension, induced by noradrenaline given intravenously. Identical measurements were made in 11 subjects before and during concomitant local intra-arterial infusion of noradrenaline without change in blood pressure and eight subjects were studied during saline infusions. 3. One hour of sustained hypertension (diastolic blood pressure > 95 mmHg) significantly attenuated both forearm blood flow (17.4 +/- 6.8 versus 27.4 +/- 6.8 ml.min-1.100 ml-1 tissue at baseline, P < 0.05) and forearm vascular resistance decrease (3.2 +/- 0.87 versus 7.4 +/- 2.5 units at baseline, P < 0.05) during methacholine infusion. These attenuations were significantly more pronounced for methacholine than for sodium nitroprusside (P < 0.05). In contrast, local intra-arterial noradrenaline infusions impaired vasodilatation induced by methacholine and sodium nitroprusside to a similar extent. Saline infusions did not change either EDV or EIDV. 4. Thus, an acute rise in blood pressure to hypertensive levels induced by noradrenaline impaired EDV more than EIDV in otherwise normotensive subjects, while no such selective effect of local noradrenaline was seen, suggesting that a high blood pressure impairs endothelial vasodilator function.