The effect of lumbar extradural analgesia on intervillous blood flow (IBF) during labour was studied in 26 healthy parturients using an i.v. bolus injection of xenon-133. There was a 19% decrease (n.s.) in mean IBF in six parturients (non-extradural control group). Mean IBF increased by 37.5% when 0.25% bupivacaine 10 ml was used and by 35.2% when 2% 2-chloroprocaine 10 ml was used (n.s.). When the two extradural groups were combined, the mean difference between IBF1 and IBF2 was 45 +/- 112 ml min-1 dl-1. This increase is statistically significant (P less than 0.05). The improvement in IBF after extradural block was considered to be a result of the decreased uterine vascular resistance, as no significant changes were observed in arterial pressure, uterine activity or uterine tone.