Recent studies on the association between particular single nucleotide polymorphisms of serine-threonine kinase with no lysine (K) 4 gene (WNK4) and essential hypertension have yielded controversial results. Here, frequencies of Ala589Ser polymorphism within exon 8 of the WNK4 gene were assessed among 259 unrelated ethnic Chinese patients with essential hypertension and 235 strictly matched normotensive controls. All subjects were derived from a relatively isolated population identified in the Kerqin desert region in Zhangwu county of Liaoning, northeastern China, which features a dry climate and the people having a high dietary salt intake, in addition to a significantly higher prevalence (similar to 35%) of essential hypertension. Genotypes were verified with polymerase chain reaction-restriction fragment length polymorphism and confirmed by direct sequencing. Expression pattern and regulatory mechanisms of the WNK4 gene were also explored using Northern blotting and in vitro hormone stimulation assays. Strong associations between the Ala589Ser polymorphism and both raised systolic and diastolic blood pressures were identified. In addition to the kidneys, WNK4 gene expression was also found in many other organs. Several cis-acting elements had been discovered in the promoter region of the gene. As revealed by preliminary experiment, various hormones can down-regulate the expression of WNK4, among which glucocorticoid hormone seems to act in a dose-dependent manner. The WNK4 gene probably plays an important role in the pathogenesis of essential hypertension. As a missense mutation, the Ala589Ser polymorphism may bring changes to the enzyme's function(s), resulting in increased susceptibility to the disease.