Traditional sphygmomanometric measurements may inaccurately reflect the actual blood pressure level over a 24-h period. This is due to several factors which are known to affect cuff blood pressure readings, including the limited number of readings obtainable throughout the 24 h and the alerting reaction and pressor response induced in patients by the presence of the physician. Twenty-four-hour ambulatory blood pressure monitoring has been reported to be superior to isolated cuff blood pressure readings in the diagnostic evaluation of hypertension and in assessing the blood pressure response to treatment. It does not trigger any emotionally induced pressor reaction and is able to provide a dynamic evaluation of blood pressure profiles over 24 h. The latter feature is particularly important in assessing the ability of once-daily antihypertensive treatment to reduce and maintain blood pressure at an appropriate level throughout the 24-h period. Studies to date using ambulatory blood pressure monitoring techniques suggest that once-daily administration of certain ACE inhibitors is capable of providing this long-term control of blood pressure. The 24-h antihypertensive action exerted by once-daily administration of ACE inhibitors is characterized by balanced blood pressure control throughout the day and night, and treatment does not appear to alter the neural mechanisms responsible for cardiovascular homeostasis, as suggested by the fact that these drugs have been shown not to affect 24-h blood pressure and heart rate variability. Furthermore, during administration of ACE inhibitors the sensitivity of arterial baroreceptor control of circulation is unaltered or even enhanced. These observations emphasise the potential importance of long-acting ACE inhibitors in the control of arterial hypertension.