As a key enzyme of the renin-angiotensin-aldosterone system, the renin gene (REN) is a good candidate quantitative trait locus that may be implicated in the molecular etiology of essential hypertension. Among mixed reports on the subject, a REN MboI restriction fragment length polymorphism has been shown to be significantly associated with a family history of hypertension in a Japanese population. We show here that the REN MboI dimorphic site is located in the ninth intron of the gene, and we describe a polymerase chain reaction-based assay for detection of this site. We investigated MboI genotype distributions in 331 hypertensive and 279 normotensive subjects from the United Arab Emirates (UAE), a genetically homogeneous ethnic population with no history of smoking or alcohol consumption. A statistically significant association was found between alleles on which the MboI site is present and clinical diagnosis of essential hypertension, indicating that 1) the presence of the MboI site is a marker for susceptibility to hypertension in the UAE (the associated odds ratio is 3.16); and 2) variations of the REN (or of a nearby) gene that may be in linkage disequilibrium with this marker play a role in the development of essential hypertension in the UAE.