Blood pressure fluctuates continuously over time, either spontaneously or in response to a variety of external stimulations. The occurrence of these continuous and often marked blood pressure variations is not only of pathophysiologic interest, but it may also have a clinical relevance. Indeed, it has been shown that the occurrence of pronounced blood pressure changes at the time of the physician's visit may introduce errors in the diagnosis of hypertension and in the assessment of the efficacy of antihypertensive treatment. Moreover, several studies have reported that the end-organ damage of hypertension is significantly and independently related to the degree of blood pressure variability during the day and night. This was shown by reports that assessed blood pressure variability by a variety of different methods, i.e. by computing the 24 h or daytime blood pressure standard deviation, the degree of morning blood pressure rise or that of night-time blood pressure fall, the frequency of blood pressure peaks over the 24 h, and the blood pressure increases under stressful conditions or during physical exercise. Results from a recent follow-up study have provided evidence that the degree of blood pressure variability may also have prognostic relevance in hypertensive patients. Thus, optimal antihypertensive treatment might also need to reduce the degree of blood pressure fluctuations together with the 24 h average blood pressure levels. Until recently, however, available antihypertensive drugs have been ineffective in buffering blood pressure variability or have even been responsible for an increase in the degree of blood pressure fluctuations. Further studies are needed to assess whether recently developed antihypertensive agents, and in particular those able to induce a smooth reduction in blood pressure over the 24 h or to modulate the sympathetic influences exerted on the cardiovascular system, may represent better tools to reduce the magnitude of an enhanced blood pressure variability in hypertensive patients over the 24 h. Recent progress in technology has offered us more powerful tools to address this issue. They include devices for continuous noninvasive ambulatory blood pressure monitoring (Portapres, TNO), and techniques for a more comprehensive analysis of all components which contribute to overall blood pressure variability (broad-band spectral analysis).