In a consecutive series of 1,201 singleton pregnancies with pre-eclampsia, the onset occurred during labour in 290 (24.1%). There was no difference between the primiparous and parous patient in this respect (25.9% v 20.7%; P less than 0.10). The tendency for pre-eclampsia to develop during labour increased with advancing maturity of the pregnancy and seldom occurred before 38 weeks of gestation; this was again equally true of the primiparous and parous patient, as was the incidence of severe hypertension (diastolic pressure greater than 110mm Hg) (36.1% v 34.1%). The high incidences of severe hypertension (35.5%), proteinuria (41.7%), and eclampsia (2.1%), and the 1 maternal death testified to the severity of the disease process and the need for aggressive management. After delivery, the clinical signs tended to subside rapidly, but the early third stage of labour was a time of maternal risk, irrespective of whether ergometrine or Syntocinon was the oxytocic agent administered. Analysis of perinatal results showed that the risk to the fetus was minimal.