There is a convincing volume of evidence to support the contention that optimal control of blood pressure should be based upon therapeutic strategies that consistently reduce blood pressure in a smooth and consistent fashion. Attention has, therefore, been focused on calculation of trough:peak ratios and, alternatively, the smoothing index as methodologies for defining the duration of action of an antihypertensive drug and for discriminating among alternative treatments. Acceptable accuracy and reproducibility for trough:peak ratio have been demonstrated in the controlled environment of a research unit. In contrast, trough:peak ratios from ambulatory blood pressure recordings exhibit wide inter-patient variability. With respect to clinical validity, unlike trough:peak ratio, the smoothing index has been shown to be correlated to the regression of left ventricular hypertrophy induced by treatment. Overall, neither index has been proven to offer definitive superiority and hence it is reasonable to suggest that the two are complementary.