The adenosine A2a receptor (A2aAR) gene is thought to be involved in essential hypertension because adenosine elicits vasodilation and decreases arterial blood pressure via this receptor, and because disruption of the A2aAR gene increases blood pressure in mice. Therefore, using a restriction fragment length polymorphism (RFLP) of the A2aAR gene, we performed an association study in patients with essential hypertension. One hundred forty-two patients with essential hypertension and 142 age-matched subjects with normal blood pressure were studied. Polymerase chain reaction (PCR) was applied to amplify the T1083C polymorphic site in the A2aAR gene, and restriction analysis of the PCR product was employed to score the T and C alleles. Overall distributions of allele frequencies in the two groups were not significantly different. Thus, the alleles detected by this RFLP polymorphism in the A2aAR gene are not associated with essential hypertension.