The invasive and non-invasive techniques now available for automatic monitoring of blood pressure have provided new sets of physiological as well as diagnostic and therapeutic data. Recordings of blood pressure variations over a 24-hour period have shown that it increases during the day and decreases at night, that these physiological changes are more pronounced in the elderly than in young subjects and also that they depend on the degree of physical activity. The clinical applications of these techniques rest on the possibility of recording a blood pressure-activity profile over time, in order to speak, ultimately, in terms of blood pressure load activity. By reference to a normal blood pressure profile, genuinely hypertensive subjects can be differentiated better from those overactive, hyperemotional subjects who are perhaps not suffering from true hypertension. Finally, 24-hour recordings repeated over periods of several days or weeks enable the clinicians to assess therapeutic effectiveness and to envisage an authentic chronotherapy.