Measurements made at baseline permitted assessment of whether the hypothesized positive relation of lithium countertransport to blood pressure was independent of such factors as age, sex, body mass index, alcohol intake, plasma uric acid, glucose, family history, and other variables generally associated with blood pressure. The relationship between 5-year changes in these factors, change in lithium countertransport, and in blood pressure were also examined. Several additional important unresolved questions on the epidemiology of blood pressure and hypertension were explored: the role of macronutrients and micronutrients in lithium countertransport and its change; red blood cell sodium and potassium concentrations and their relation to blood pressure; possible differences in calcium metabolism between hypertensives and normotensives; genetic polymorphisms related to lipid-lipoprotein metabolism and possible influence on blood pressure; patterns of blood pressure change in the elderly, the 639 and 341 persons age 65-74 and over 75, respectively, at baseline. Coronary heart disease incidence was also studied.