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Epidemiologic studies have demonstrated that the peak incidence of most types of cardiovascular disease follows a circadian (24 h) pattern. Ambulatory monitoring studies have documented a reproducible 24 h rhythm for blood pressure, characterized by a period of low values during sleep, an early-morning increase in pressures, and a plateau period while the individual is awake and active. Hypertensive patients who display the typical nocturnal decrease in blood pressure are termed ‘dippers’, whereas patients in whom the nocturnal decrease in blood pressure is absent or blunted are termed ‘non-dippers’. The circadian rhythm may be influenced by demographic, neurohormonal, and pathophysiologic factors. The non-dipper profile appears to be of prognostic significance because it is associated with increased target-organ damage and a worsened cardiovascular outcome. Chronotherapy is a new pharmacologic concept whereby medication is delivered at a time and in a concentration that varies according to physiologic need during the dosing period. Of greatest interest is the reduction in blood pressure during the early-morning blood pressure surge, as that time is associated with an increased risk for myocardial infarction and stroke. Factors that may increase the early-morning blood pressure include activation of the sympathetic nervous system and the renin-angiotensin-aldosterone system. In the near future, the benefits of a chronotherapeutic approach to the management of hypertension should be elucidated by large-scale outcome studies.