The purpose of this article is to review some clinical and fundamental evidence that hypertension-induced arterial wall hypertrophy at the site of large and medium-sized arteries is not necessarily associated with a decreased arterial distensibility and increased elastic modulus, and to demonstrate the opposing effects of aging and hypertension-induced hypertrophy on the arterial mechanics in vivo. in the studies reported here, the elastic properties of large and medium-sized arteries were noninvasively assessed from the simultaneous measurement of internal diameter and blood pressure inside the systolic-diastolic range. The distensibility of a medium-sized artery, the radial artery, in untreated essential hypertensive patients was not significantly different from that of normotensive control subjects when the two groups were compared at their respective mean arterial pressures. Despite increased wall thickness, the stiffness of the radial artery wall material, assessed by the incremental modulus of elasticity (Young's modulus), was not increased in hypertensive patients. At the site of a larger, more elastic artery, such as the common carotid artery, distensibility of hypertensive patients was significantly lower than that of normotensive subjects when the two groups were compared at their respective mean arterial pressures, but distensibility at 100 mm Hg was not significantly different between the two groups. Aging may alter distensibility independently of blood pressure, because carotid distensibility at 100 mm Hg was negatively correlated with age. In spontaneously hypertensive rats the elastic modulus of the common carotid artery wall material was not significantly different from that of Wistar-Kyoto rats at a given circumferential stress.(ABSTRACT TRUNCATED AT 250 WORDS)