This demonstration project provides for central collection of a standard set of clinical data for patients at some of the Hypertension Screening and Treatment Program clinics, thereby setting up a national data base on the treatment of hypertension. The primary objective of this project is to demonstrate the value of establishing this type of database. The database is being used to estimate the average annual cost of different antihypertensive regimens, to determine the cost-efficacy of different therapies and the least expensive effective therapy and to address some major unanswered clinical questions that require large populations and long-term patient care data. There are currently 13 medical centers participating.