The static elasticity (Ep) (Peterson) and the characteristic impedance of the aorta (Zo) (Mac Donald) were evaluated by the simultaneous measurement of the pressure and diameter of the ascending aorta in 30 patients: 18 subjects were free from any aortic pathology (Group I), subjects had persistant arterial hypertension (Groupe II), and 3 subjects had aortic incompetence (Group III). In the group I patients, Ep increased significantly with age, and with the aortic pressure and diameter. In groupe II, Ep increased significantly only with aortic pressure. A narrow correlation was found between the characteristic impedance of the ascending aorta and the systolic ejection resistance, except in those patients with aortic incompetence, in whom it seems that Zo is a better measure of ejection resistance. In the group I patients, impedance increased significantly with age. No significant difference was found in the characteristic impedence between patients of groups I and II, the aortic diameter being greater in the latter group.