A non-invasive Doppler ultrasound technique for the assessment of aortic compliance based on the in vivo measurement of pulse wave velocity along the thoraco-abdominal aortic pathway is described. An approach for correcting for the effect of blood pressure on aortic compliance is considered. The derivation of an index of distensibility, Cp, which is independent of blood pressure is provided and applied to data collected from 58 normal, healthy volunteers. Medical disorders such as atherosclerosis, diabetes mellitus and familial hypercholesterolaemia have all been shown to affect arterial distensibility. We suggest that the clinical measurement of Cp may be a useful, non-invasive tool for assessing such patients' susceptibility to atheromatous arterial disease as well as for monitoring their response to therapy.