This paper outlines the advantages of ambulatory blood pressure monitoring (ABPM) in the evaluation of the efficacy of antihypertensive drugs. The main advantage is that ABPM allows the antihypertensive effect of a drug or drug regimen to be determined in daily life conditions and to uncover whether the treatment employed is associated with untoward hypotensive episodes. Furthermore, ABPM facilitates the design of studies on antihypertensive drug efficacy because the 24 h mean blood pressure is devoid of a placebo effect and its reproducibility is much greater than office blood pressure. This has permitted demonstration of the efficacy of several antihypertensive drug regimens, including diuretic studies, based on relatively small numbers of subjects. A further advantage of ABPM is that it allows drug treatment efficacy to be evaluated in relation to blood pressure variability, another possible determinant of the organ damage related to hypertension.