From the parallel group design to the crossover design, and from the group approach to the individual approach. The consequences of heterogeneity in response to antihypertensive drugs for the clinical development programs of new antihypertensive drugs and for the care of the individual hypertensive patient have not previously been sufficiently recognized. They play a role in the inappropriate choice of too-high daily doses of some antihypertensive drugs at the end of extensive international development programs. They are also implicated in the insufficient control of blood pressure observed in the long-term multicenter trials in hypertension, where some patients have been treated for several years with drugs that were not the most appropriate for their disease and which did not adequately control their blood pressure. In addition to the parallel group studies, the use of double-blind two-period or multiple period crossover designs can provide valid data for the dose-finding of new antihypertensive drugs and their comparative evaluation. At the end of the trial, these designs also offer each patient the opportunity to be treated with the right dose of the drug most appropriate for his or her disease. 