A common protocol was followed in this cross-sectional study. Data were collected on blood pressure and on electrolyte and creatinine excretion in timed 24-hour urine and casual urine samples. Data were also collected on age, sex, height, weight, alcohol intake, diet, drug treatment for hypertension, family history of cardiovascular disease, contraceptive pill use, smoking, physical activity, and social and educational status. Urine specimens were analyzed for sodium, potassium, chloride, calcium, magnesium, and creatinine in the central laboratory at St. Raphael University in Leuven, Belgium. The data were coordinated at the London School of Hygiene and Tropical Medicine, London, England. The data from the University of Mississippi were analyzed separately using uric acid as a covariate.