Hypertension is a condition where adrenergic responsiveness, sympathetic activity and adrenoceptors are somewhat altered. Many techniques are available to assess human sympathetic nervous system activity. They each present limitations and disadvantages. Characterization and subdivision of the alpha and beta-adrenoceptors, according to their localization and answer to different agonists, was facilitated in recent years by the extensive use of pharmacological and molecular biology techniques. Some adrenoceptor studies were conducted on animal models, human tissues and peripheral blood cells to assess their changes in various forms and stages of hypertension. Our group has pointed out that alpha1-adrenergic receptors expressed by human peripheral blood lymphocytes underwent changes of density in essential hypertensives, compared to normotensive control subjects. The importance of these findings could provide an assessment of alpha1-peripheral receptors with possible future clinical implications in the pathophysiology and treatment of hypertension.