To assess whether aerobic exercise training is an effective and an alternative method to control blood pressure (BP) in hypertension, 32 uncomplicated, never treated patients suffering from mild-to-moderate essential arterial hypertension (EAH) were included in an aerobic exercise training program using a regular standardized cycle ergometer exercise for 3 months. In all EAH patients, before and after the exercise training period, ambulatory BP monitoring (ABPM) was performed and several metabolic variables were assessed. Before exercise, in 20 EAH patients, a 48-h ABPM showed a normal day-night rhythm, with nocturnal BP decrease, according to a dipper-type hypertension, whereas in 12 EAH patients 48-h ABPM profile indicated a nondipper-type hypertension. After exercise, EAH dippers presented a significant decrease in the daytime systolic and diastolic BP, whereas EAH nondippers did not show any change in daytime and nighttime systolic and diastolic BP. Our study confirms the controversy about the postulated BP lowering effect of dynamic exercise in EAH patients, in the sense that only EAH dipper patients seem to obtain a beneficial diurnal lowering BP effect deriving from exercise, possibly through a reduction in sympathetic tone. On the contrary, physical activity seems to fail in reducing diurnal and nocturnal BP values in EAH nondippers, suggesting that in nondipper-type hypertension, other "masking" endogenous or exogenous factors could interfere with and prevail over the adrenergic-vagal balance that modulates the day-night BP synchronism.