The need to investigate the elastic properties of arterial vessels‘in situ’for the early recognition of degenerative disorders in arteries has long been apparent. Volume pulses in defined segments of arteries can be evaluated for this purpose, and the present paper contains a survey of earlier attempts to quantify volume pulses by means of ultrasound. A presentation is given of a recently developed digital system, comprising a phase-locked echo tracker, capable of monitoring non-invasively the diameter and its pulsatile changes of a selected artery along two chosen image lines of a linear array ultrasound scanner. The physical limitations of tracking fastmoving ultrasound echoes by means of phase-locked range gating are reported and the advantage is emphasized of using a gate length of one full period. This system has been calibrated, tested and applied in measurements of pulse wave pattern and propagation velocity in the descending aorta of human foetuses in the last trimester of gestation. The present high-resolution echo-tracking method has yielded reproducible results in the foetus and appears suitable also for screening studies on adult vessels.