Serial haemodynamic investigations were performed in 32 women who were allocated randomly to receive either spinal or extradural anaesthesia for elective Caesarean section. Cardiac output was measured by Doppler and cross-sectional echocardiography at the aortic valve. Doppler flow velocity waveforms were recorded also from the umbilical artery. Preloading with Ringer lactate solution 1 litre increased cardiac output in both groups. After injection of bupivacaine, cardiac output remained increased in the extradural group, but decreased in the spinal group. This was associated with an increase in umbilical artery pulsatility index in the spinal group. Umbilical artery pH was less in the spinal group (7.22 vs 7.27), although no neonate was depressed at birth. The maximum percentage change in cardiac output and umbilical artery pulsatility index correlated with umbilical artery pH (r = 0.54, r = 0.72, respectively). There was no significant correlation with change in arterial pressure.