OBJECTIVES: Hypertension is known to decrease arterial elasticity and systemic compliance. However, the arterial tree is not a homogeneous system, and whether a distal medium-sized artery such as the radial artery behaves like proximal arteries has not been determined. The aims of the present study were, first, to characterize non-invasively the mechanical properties of the radial artery through the determination of the pressure-diameter curve, the distensibility-pressure curve and the compliance-pressure curve, and, secondly, to compare untreated hypertensive patients with normotensive subjects. METHODS: A new high-precision echo-tracking device was developed which allows the diameter of peripheral arteries to be measured continuously. By relating the changes in internal diameter (cross-sectional changes) to those in blood pressure, the cross-sectional arterial compliance could be determined. PARTICIPANTS: Seventy-eight untreated mild or moderate essential hypertensive patients aged 24-78 years were compared with 44 normotensive subjects aged 22-81 years. In order to increase the database and provide independent assessments of the variables examined, the cross-sectional study was performed independently using a standardized procedure in three different research centres. RESULTS: The major finding was that diameter, distensibility and compliance of the radial artery of hypertensive patients were not significantly different from those of normotensive controls when the two populations were studied at their mean arterial pressure. Furthermore, when the two populations were compared for the same level of blood pressure, using distensibility--and compliance--pressure curves, it was clear that isobaric distensibility and compliance of hypertensives were not significantly lower than those of normotensives, being either unchanged or higher. CONCLUSIONS: These findings are in contrast with the well-known decrease in compliance of proximal large arteries due to hypertension. Whether such a difference between proximal large arteries and distal medium-sized arteries may be related to the structural vascular changes observed with long-standing hypertension is still difficult to analyse in humans, and requires further investigation.