Background: Dynamic exercise acutely and transiently lowers resting blood pressure in hypertensive men and is termed postexercise hypotension (PEH). We examined 18 premenopausal women (7 hypertensive and 11 normotensive) to determine if PEH occurs in women and to elucidate possible hemodynamic and hormonal mechanisms. Methods and Results: Patients wore an ambulatory blood pressure monitor throughout the day after 40 minutes of a rest sham session and 40 minutes of cycle exercise, of which 30 minutes was performed at 60% of maximal oxygen consumption. Cardiac output and total systemic vascular resistance were determined by Doppler echocardiography before and 15 minutes after sham and exercise. Catecholamines, plasma renin activity, and β-endorphin were measured over this same period. PEH occurred only in the hypertensive women. Systolic, diastolic, and mean arterial blood pressure decreased in the hypertensive women by a mean of 9.5 ± 2.8 mm Hg (P < .01), 6.7 ± 2.4 mm Hg (P < .05), and 7.7 ± 2.4 mm Hg (P < .05), respectively, for up to 7 hours after versus before exercise, whereas blood pressure was similar in the normotensive women (P > .05). After exercise, total systemic vascular resistance was lower (P < .01), and cardiac output, catecholamines, and plasma renin activity were greater (P < .01) than before exercise in both groups of women. Conclusions: PEH was observed for up to 7 hours after exercise in mildly hypertensive women and was not explained by the hemodynamic and hormonal adjustments that occurred after exercise. The magnitude and duration of PEH may be sufficient to normalize the blood pressure of certain hypertensive women throughout most of the day. (Am Heart J 1999;138:916-21.)