The primary goal of antihypertensive therapy is to restore blood pressure to normal levels and to prevent the complications associated with hypertension. In order to maximize these goals by improving patient compliance, clinical researchers have focused on developing antihypertensive agents that can be given once daily. These agents provide many advantages over multiple-dose daily therapies, but it should not be assumed that they are all equivalent in providing adequate blood pressure control over the full 24-h dosing interval. Ambulatory blood pressure monitoring has uncovered important differences in commonly used once-daily therapies and has provided additional insights into the cardiovascular risks associated with high blood pressure loads and blood pressure variability. In addition to ambulatory blood pressure monitoring data, the calculated trough:peak ratio provides useful information on an agent's ability to provide smooth and consistent blood pressure control. Using such assessments, it has been found that agents with a trough:peak ratio > or = 0.50 are better able to control blood pressure over the full 24h while maintaining natural circadian patterns. Ambulatory blood pressure monitoring studies assessing a recently introduced class of antihypertensive drugs, the angiotensin receptor blockers, have demonstrated 24-h efficacy with once-daily dosing, particularly with the newer agents.