Although the historical debate between Pickering and Platt has never been settled, most scientists have felt that hypertension should not be defined as a disease state, qualitatively different from normotension with a sharp dividing line in between them. Still, in clinical practice, there is a need for well defined limits which one should initiate therapeutic actions that should not be taken below such a limit. In fact, in trying to escape to setting up a sharp limit, clinicians have tried to find a level above which benefits of decreasing blood pressure could outweigh the potential harm caused by the therapeutic interventions. However even in that way, finding such a limit is a most difficult enterprise; it has necessitated many large trials which certainly have not resolved yet all our questions. First, one should realize that blood pressure by itself is not a constant value; following blood pressure over a certain period shows its large variations from "normotensive" ranges to clearly "hypertensive" levels in the same individual. As soon as one is spoiled by this type of information, it becomes hardly conceivable to define someone's blood pressure without ambulatory recordings of some kind. This is also valid for finding the above mentioned limit of therapeutic benefit; an European International multicenter studied is being set up in this respect (HOME BP). Moreover, whatever the definition of blood pressure, its relationship to mortality, morbidity and organ damage, also, is not a constant one.(ABSTRACT TRUNCATED AT 250 WORDS)