Chronopharmacology in hypertension management aids clinical decision making on the best administration times of antihypertensive drugs to achieve optimum circadian blood pressure (BP) control. The aims of the study were to test the effect on 24-hour BP profile of valsartan and amlodipine; to compare the effects of morning versus evening dosing on circadian BP and to compare the effects of valsartan and amlodipine between males and females. Patients suffering from essential hypertension who were prescribed once daily valsartan or once daily amlodipine participated in the study. Recruited patients had their 24h BP profiles measured using an ambulatory blood pressure monitor (ABPM).