Ambulatory blood pressure is more closely related to the end organ damage of hypertension than clinic blood pressure is. This is the case not only for left ventricular hypertrophy, but also for an index of renal involvement such as microalbuminuria. The closer correlation of ambulatory blood pressure with end organ damage characterises not only the 24 hour average value but also, to a similar extent, day-time and night-time average blood pressure, while the clinical importance of the difference between day and night blood pressure is still a matter of controversy. A more promising index derived from ambulatory blood pressure recordings seems to be blood pressure variability, which in preliminary studies has been shown to display an independent correlation with the end organ damage of hypertension.