Five-year re-examination of the population of Gubbio, a town in north central Italy, aims at testing prospectively hypotheses related to the role of sodium-stimulated lithium countertransport (LCT), measured in 1983-85, in subsequent change in blood pressure as well as incidence of hypertension. In this large population sample (5,376 persons age 5-90, 92% of the identified population), measurements made at baseline also permit assessment of whether the hypothesized positive relation of LCT to blood pressure (BP) is independent of such factors as age, sex, body mass index, alcohol intake, plasma uric acid, glucose, family history, and other variables generally associated with BP. The relationship between 5-year changes in these factors, change in LCT, and in blood pressure will also be examined. Advantage will also be taken of this large data base to explore several additional important unresolved questions on the epidemiology of blood pressure and hypertension: the role of macronutrients and micronutrients in LCT and its change; red blood cell sodium and potassium concentrations and their relation to BP; possible differences in calcium metabolism between hypertensives and normotensives; genetic polymorphisms related to lipid-lipoprotein metabolism and possible influence on BP; patterns of blood pressure change in the elderly (i.e., the 639 and 341 persons age 65-74 and 75+, respectively, at baseline). The central focus of the study in Gubbio is on hypertension, in part because the prevalence of high blood pressure is high in this Italian town. But, in addition, it is planned to take advantage of the unusual opportunity presented by the Gubbio situation to study coronary heart disease incidence in this population whose coronary risk factors have apparently changed, to reach levels equal to or above those currently prevalent in the United States. This next phase of the study will be done in collaboration with colleagues in Gubbio, Rome, and Naples. It is anticipated that successful accomplishment of the 5-year follow-up examination will lay the foundation for further long-term follow-up.