The established technique of investigating peripheral arteries by continuous-wave Doppler ultrasound was first applied to obstetrics by FitzGerald and Drumm in 1977. Since that time, each year has seen an increasing number of reports regarding obstetric Doppler, but assessment of its true value in pregnancy management, by large prospective randomized trials, is still awaited. Continuous-wave Doppler ultrasound is a relatively simple and inexpensive technique, ideal for screening the uterine and umbilical arterial circulations without the necessity for concurrent ultrasound imaging. However, difficulties in interpretation and analysis of the displayed Doppler-shifted frequencies, as well as the limited number of reports on the performance characteristics of Doppler ultrasound instruments, may well have contributed to the slowness with which the technique has been taken up for study. Continuous-wave Doppler systems designed for obstetric use have recently become available and the Vasoflo-3 (Oxford Sonicaid, Chichester, Sussex) has a microprocessor which makes the instrument very versatile. I shall review the technique of continuous-wave Doppler ultrasound measurement in obstetrics, with particular reference to measurement variation, in the light of our experience with the Vasoflo-3 (Figure 1). I shall then briefly summarize a few of the reports which have used continuous-wave Doppler ultrasound in obstetrics.