SummaryOne hundred and one pregnant women with hypertensive disorders were prospectively studied with doppler ultrasound flow velocity waveforms of the umbilical artery. Results were withheld from the obstetricians so that the test did not influence obstetric management. It was found that the resistance index of the umbilical artery was higher in patients with proteinuric pregnancy induced hypertension and in patients with chronic hypertension than in patients with non-proteinuric pregnancy induced hypertension. Patients with an abnormal resistance index were more likely to be delivered prematurely, have small for dates babies, have fulminating hypertension and have an abnormal antepartum cardiotocogram. Thirteen patients had a pathological antenatal cardiotocogram and they all had an abnormal umbilical artery flow velocity wave form when the cardiotocogram was normal.