This study was done to assess the antihypertensive efficacy of once-daily valsartan 20 mg, 80 mg, 160 mg, and 320 mg over 24 hours using ambulatory blood pressure monitoring (ABPM). A total of 217 adult outpatients with uncomplicated essential hypertension (office mean sitting diastolic blood pressure [DBP] of > or = 95 to < or = 115 mm Hg) participated in this multicenter, double-masked, placebo-controlled study. Patients were randomized to receive valsartan 20 mg, 80 mg, 160 mg, 320 mg, or placebo for 8 weeks. Twenty-four-hour ABPM was done at baseline and after 8 weeks of treatment. All valsartan doses produced significant decreases in average ambulatory systolic blood pressure (SBP) and DBP over 24 hours compared with placebo. A trend to greater reductions compared with placebo was observed for doses of valsartan 80 mg and greater (80 mg, -6.61 mm Hg DBP, -11.04 mm Hg SBP; 160 mg, -5.51 mm Hg DBP, -10.61 mm Hg SBP; 320 mg, -8.44 mm Hg DBP, -14.34 mm Hg SBP) compared with valsartan 20 mg (-3.52 mm Hg DBP, -5.92 mm Hg SBP). Valsartan produced consistent reductions compared with placebo during both day (> 6 AM to < or = 10 PM) and night (> 10 PM to < or = 6 AM). However, in all groups, the circadian pattern of blood pressure over 24 hours was preserved and was similar to that observed at baseline (but shifted into the normotensive range in a parallel fashion). The data show that single daily doses of valsartan 80 mg and greater provide effective control of both DBP and SBP over a 24-hour period without loss of diurnal variation.