This study of 10,000 persons in 1600 nuclear families and 2500 persons in 50 extended pedigrees will ellucidate the mechanisms by which genetic and environmental factors interact to control blood pressure and lead to hypertension. Utah investigators will analyze all data collected from nuclear family relatives (parents, siblings, or children) of participants in a clinical trial of preventing hypertension among high risk individuals at 13 clinical centers of the Hypertension Detection and Follow-Up Program (HDFP). These analyses will determine the extent to which genetic factors may explain or predict different blood pressure responses to the weight reduction and sodium restriction interventions used to prevent hypertension in the clinical trial. In addition to analyzing nuclear family data from all other centers, the Utah investigators will conduct a clinical screening study of 2500 subjects in 50 pedigrees of 4-5 generations, most of them ascertained with the help of the population-based computer file of Utah pedigrees (currently containing over 1,000,000 persons). Data collection will include detailed questionnaires of lifestyles and habits; height, weight, skinfolds; multiple blood pressure measurements before and after special stress tests; multiple 12-hour urine samples of sodium, potassium, creatinine, aldosterone, kallikrein; and blood samples for creatinine, sodium, potassium, uric acid, cholesterol, renin, hematocrit, and glucose one hour after a glucose level. These detailed data collected from subjects in 50 large pedigrees can be analyzed to determine the etiological factors for blood pressure and hypertension including: mechanisms of genetic transmission (few major genes vs. Galtonian polygenic, gene frequencies, number of alleles and loci, degree of dominance); the role of environmental factors (such as sodium and calorie intake, stress etc.) which interact with genes or affect their penetrance; and the degree of heterogeneity between pedigrees.