There are many important uses of biomarkers in drug development. An area of particular interest is the use of biomarkers as surrogate end points. Only a small minority of biomarkers are established surrogate end points. Blood pressure is an example of a surrogate end point accepted by both clinicians and regulators. It was a plausible surrogate because of the large epidemiologic databases demonstrating a correlation between elevated blood pressures and adverse cardiovascular outcomes. That plausibility has been supported, however, by the numerous placebo-controlled outcome studies evaluating several pharmacologically distinct agents that showed an effect on stroke and coronary heart disease outcomes from lowering blood pressure.