Background. Previous studies suggest that vascular endothelial function may be impaired in essential hypertension. Although muscarinic agonists dilate blood vessels by releasing an endothelium-derived relaxing factor closely related to nitric oxide, nitroprusside dilates vessels by a mechanism that is independent of the endothelium. The finding of an impaired response to muscarinic agonists but a normal response to nitroprusside in patients with hypertension has suggested that endothelial function is abnormal in hypertension. Methods. We reassessed this issue by measuring forearm blood flow by plethysmography during the infusion of vasodilators into the brachial arteries of 95 subjects: 37 normotensive controls (mean [±SE] arterial blood pressure, 92±1 mm Hg) and 58 patients with essential hypertension (mean arterial blood pressure, 121±1 mm Hg). Results. In an initial study, vascular responses to the vasodilators carbachol and nitroprusside were similar in normotensive controls (n = 19) and hypertensive patients (n = 17). We wondered whether this might be attributable to the use of previously untreated patients or to the choice of carbachol as the muscarinic agonist. However, we found that the vasodilator responses to nitroprusside, acetylcholine, carbachol, and isoproterenol were also similar in separate groups of normotensive controls (n = 18) and hypertensive subjects, whether the subjects had never been treated for hypertension (n = 24) or had had therapy withheld for two weeks (n = 17). The 95 percent confidence intervals for the difference between the controls and hypertensive patients in the ratio of endothelium-dependent vasodilatation induced by acetylcholine or carbachol to endothelium-independent vasodilatation induced by nitroprusside were -14 to +23 percent for acetylcholine and -13 to +12 percent for carbachol. Conclusions. In contrast to previous studies, our findings suggest that selective impairment of the responsiveness of the forearm vasculature to muscarinic agonists is not universal in patients with essential hypertension.