The primary physiological agents for adrenergic receptors are only two, epinephrine and norepinephrine, which have been used to differentiate alpha- and beta-adrenoceptors. The pharmacological properties can distinguish subtype alpha 1-, alpha 2-, beta 1- and beta 2-receptors. Recently additional subtypes have been characterized by radioligand binding techniques and molecular biological techniques. Molecular mechanisms of regulation as well as regulatory site of gene expression of alpha-adrenergic receptors has been extensively studied. In addition, the association analysis of alpha 2-adrenergic receptor gene RFLP in essential hypertension has been performed. Eventhough we could not find any association of an alpha 2 C10-Bsu36I RFLP with essential hypertension in Japan, the finding showed significant ethnic RFLP difference at the gene locus for alpha 2 C10. The association of alpha 2 adrenergic receptor RFLP with blood pressure has been also studied using F2 generations of SHR and WKY and Dahl salt sensitive rats and resistant rats. Further studies are now in progress to clarify the role of these alpha-adrenergic receptors in cardiovascular diseases.