Abstract--Recent studies show that healthy subjects and patients with moderate hypertension have different pressor responses to hyperventilation, depending on their sympathoadrenergic reactivity. In the present study, we investigated whether a different response to the hyperventilation test is related to differences in the daily blood pressure profiles recorded with noninvasive ambulatory monitoring. Forty-five healthy subjects and 67 patients with essential hypertension of grades 1 and 2 (Joint National Committee VI and World Health Organization) were investigated. Healthy subjects and hypertensive patients responding to hyperventilation with an increase in systolic blood pressure had, during daytime ambulatory blood pressure assessment, peak systolic blood pressure values (146.0±5.0 mm Hg, 182.2±9.0 mm Hg, respectively) similar to the hyperventilation peak systolic blood pressure values (147.2±3.5 mm Hg, 183.0±4.7 mm Hg, respectively). Hypertensive patients responding to hyperventilation with a decrease in blood pressure showed clinic systolic blood pressure values (178.4±3.2 mm Hg) higher than daytime average ambulatory systolic blood pressure (155.2±7.1 mm Hg; P<0.01). Our results indicate that a hyperventilation test yields information on daily peak blood pressure values in healthy subjects and hypertensive patients when it induces a pressor increase and can identify hypertensive patients with the so-called "white coat effect" when it induces a pressor decrease.