Essential hypertension is a complex trait which results from interaction between environmental factors and genetic factors. The aim of this study is to investigate the effects of interaction between environmental factors and genetic factors on long-term blood pressure (BP) based on two established cohorts including "the cohort of Hanzhong adolescent hypertension study" and "the cohort of Mei county adult salt-sensitive hypertension study". Firstly, the Hanzhong cohort-based follow-up study is designed to observe the track of BP during the whole life time, and to explore the effects of many risk factors (such as salt-sensitivity, obesity et al) on long-term BP and the occurrence of hypertension, and also to analyze the relationship of different polymorphisms of sodium and potassium metabolism-related gene with BP changes and target organ damages. In addition, by using DNA samples collected from subjects of "Mei county adult salt-sensitive hypertension study"in which all participants had completed a chronic salt loading and potassium intervention trial, we attempt to examine the single nucleotide polymorphisms (SNPs) of sodium and potassium metabolism-related genes, as well as the relationship between these SNPs and BP responses to dietary sodium/potassium intervention, long-term BP change, the risk of hypertension and target organ damages were analyzed. This study would enable us to further explore the etiology of essential hypertension as well as to identify new genetic markers for predicting early hypertension and target organ damage.