Three characteristics of antihypertensive medication are pivotal in therapy for a patient with hypertension: potency and efficacy, duration of action, and the incidence of side-effects. The relatively new class of AT1-receptor blockers all display placebo-like tolerability and, as a class, their antihypertensive efficacy compares well with other antihypertensive classes. However, it is unclear whether clinically important differences in duration of action and antihypertensive efficacy exist within the AT1-receptor blocker class itself. The results of a number of head-to-head clinical comparisons between these agents suggest that candesartan cilexetil and irbesartan may be more effective than the prototype AT1-receptor blocker, losartan. In addition, studies using ambulatory blood pressure recording techniques have clarified the relative durations of antihypertensive action of the AT1-receptor blockers. In particular, studies mimicking the common event of a missed or delayed dose of antihypertensive medication, show that the antihypertensive effect of candesartan cilexetil extends well beyond the 24-h dosing interval, while the effect of losartan declines rapidly over this period. The available evidence therefore suggests that significant differences in efficacy and duration of action are apparent within the AT1-receptor blocker class, and that these differences may well translate into clinically relevant differences in cardiovascular outcome.