Background The human radial artery has been proposed as an alternative to coronary grafts in subjects with coronary ischemic disease. Because this muscular artery is known to be prone to spasm, changes in its mechanical properties in response to catecholamines are important to investigate. Methods We describe a new echo-tracking technique of high resolution that allows investigation, in vitro, of the diameter and the wall thickness of arterial cylindrical segments. In addition, a classic tissue bath experiment is used to study the vasoreactivity of arterial rings. Mechanical properties of the radial artery are determined over a 0 to 200 mm Hg range of transmural pressure in the presence and absence of norepinephrine in the perfusion medium. Results With tissue bath experiments, the norepinephrine dose-response curve was characterized by an EC₅₀ value of 1.48 ± 1.09 10^-6 mol/L and a maximal developed tension at 10^-5 mol/L. The results obtained with pressurized segments gave similar results with an EC₅₀ value of 8.1 ± 2.3 10^-7 mol/L and a maximal change in diameter at 10^-5 mol/L norepinephrine. Under the influence of 10^-5 mol/L norepinephrine, the radial artery constriction reached 22%, significantly affecting the unstressed diameter. Compliance did not show any significant change in the overall transmural pressure range, whereas distensibility significantly increased and elastic modulus significantly decreased. Conclusion The study shows that the capacitive properties of the human muscular radial artery are maintained with norepinephrine not only through decreased stiffness of wall material but also through reduced unstressed diameter. Thus drugs inducing smooth muscle relaxation may be helpful in preventing radial artery spasm after coronary grafts. (Am Heart J 1998;136:624-31.)