General use of ambulatory noninvasive 24-h blood pressure monitoring in many patients has shown that new criteria for arterial hypertension are useful. A classification of circadian blood pressure in "dippers" and "nondippers" (no physiologic drop of blood pressure) needs to be specified. An altered circadian blood pressure profile, like that in nondippers, was used as a diagnostic criterion for secondary hypertension. Recent epidemiologic studies in patients with essential hypertension have shown that nondippers are at higher risk for cardiovascular complications such as myocardial infarction and cerebrovascular insult. The studies also revealed that sleep-related breathing disorders (SRBD) are characterized by increased cardiovascular risk. Increases in blood pressure caused by SRBD could be documented, with the highest amount occurring during REM sleep. A study performed in a general practice showed a high incidence (40/112) of nondippers in a group of snoring middle-aged men with obesity and daytime fatigue. This indicates diagnostic and therapeutic consequences for the control of 24-h blood pressure, including nocturnal breathing pattern and daytime symptoms due to SRBD. The goal of antihypertensive drug therapy is to reduce blood pressure significantly during the day and during the night in different stages of wakefulness and sleep. A new protocol was designed to investigate blood pressure over 24 h under a standardized load, including nocturnal hypertension. The angiotensin-converting enzyme (ACE) inhibitor cilazapril was used in this test procedure and showed a significant and clinically relevant mean blood pressure reduction of 10.0 mm Hg (versus placebo 4.3 mm Hg) over 24 h.