Administration of valsartan at bedtime as opposed to upon wakening improves the sleep-time relative blood pressure (BP) decline towards a more normal dipper pattern without loss of 24-h efficacy. Amlodipine, however, has been shown to be effective in reducing BP throughout the day and night, independent of dosing time. A large proportion of hypertensive subjects cannot be properly controlled with a single medication. However, no study has yet investigated the potential differing effects of combination therapy depending of the time-of-day of administration. Accordingly, the authors investigated the administration-time-dependent BP-lowering efficacy of valsartan/amlodipine combination. The authors studied 203 hypertensive subjects (92 men/111 women), 56.7 +/- 12.5 yrs of age, randomized to receive valsartan (160 mg/day) and amlodipine (5 mg/day) in one of the following four therapeutic schemes: both medications on awakening, both at bedtime, either one administered on awakening and the other at bedtime. BP was measured by ambulatory monitoring for 48 consecutive hours before and after 12 wks of treatment. Physical activity was simultaneously monitored every min by wrist actigraphy to accurately determine the beginning and end of daytime activity and nocturnal sleep. BP-lowering efficacy (quantified in terms of reduction of the 48-h mean of systolic/diastolic BP) was highest when both hypertension medications were ingested at bedtime, as compared to any one of the three other tested therapeutic schemes (17.4/13.4 mm Hg reduction with both medications on awakening; 15.1/9.6 mm Hg with valsartan on awakening and amlodipine at bedtime; 18.2/12.3 mm Hg with valsartan at bedtime and amlodipine on awakening; 24.7/13.5 mm Hg with both medications at bedtime; p < .018 between groups). The sleep-time relative BP decline was significantly increased towards a more normal dipper pattern only when both medications were jointly ingested at bedtime (p < .001). Bedtime dosing of the combination of the two medications also resulted in the largest percentage of controlled subjects among all the assessed therapeutic schemes (p = .003 between groups). In subjects requiring combination therapy to achieve proper BP control, the association of amlodipine and valsartan efficiently reduces BP for the entire 24 h independent of dosing time. However, the greater proportion of controlled patients, improved efficacy on lowering asleep BP mean, and increased sleep-time relative BP decline suggest valsartan/amlodipine combination therapy should be preferably administered at bedtime.