The antihypertensive efficacy of the angiotensin II receptor blocker olmesartan medoxomil has been shown to compare favourably with that of other antihypertensive agents. This randomized, double-blind study compared the antihypertensive efficacy of the starting dose of olmesartan medoxomil with that of the calcium channel blocker amlodipine besylate (amlodipine) in subjects with mild-to-moderate hypertension. Following a 4-week, single-blind, placebo run-in period, 440 subjects aged X18 years were randomized to the starting dose of olmesartan medoxomil (20 mg/day), amlodipine (5 mg/day), or placebo for 8 weeks. Subjects were evaluated by 24-h ambulatory blood pressure monitoring (ABPM) and by seated cuff blood pressure (BP) measurements at trough. The primary end point was the change from baseline in mean 24-h diastolic blood pressure (DBP) by ABPM at Week 8. Secondary end points included change from baseline in mean 24-h ambulatory systolic blood pressure (SBP) at 8 weeks, change from baseline in mean seated trough cuff DBP and SBP measurements, and response and control rates for DBP o90 and o85 mmHg. Control rates for SBP o140 and o130 mmHg were also calculated. Olmesartan medoxomil and amlodipine produced significantly greater reductions in ambulatory and seated DBP and SBP compared with placebo. Mean reductions in ambulatory and seated BP were similar between the two active agents; however, in the olmesartan medoxomil group, significantly more patients achieved the SBP goal of o130 mmHg and the DBP goal of o85 mmHg. Both drugs were well tolerated at the recommended starting dose. Although amlodipine was associated with a higher incidence of oedema, this did not reach statistical significance. Olmesartan medoxomil is an effective antihypertensive agent, with BPlowering efficacy at the starting dose similar to that of amlodipine, and is associated with more patients achieving the rigorous BP goals of SBP o130 mmHg and DBP o85 mmHg.