This article narrates the development and promotion in the 1950s and 1960s of Merck, Sharp & Dohme's Diuril (chlorothiazide), an antihypertensive drug, which played a significant role in the redefinition of high blood pressure as a widespread target for chronic pharmaceutical consumption. The joined careers of Diuril and hypertension in the late twentieth century demonstrate the connections between the clinical research, clinical practice, and marketing practices through which pharmaceuticals and disease categories come to define one another. By examining a series of internal documents preserved in the Merck Archives alongside a careful reading of the clinical literature and industry journals of the time, this article explores how the ambitions of marketers, physicians, and public health advocates found convergence in the expanding pharmaceutical prevention of chronic diseases.