In a randomized, double-blind study of 39 mothers in labour, we have compared a loading dose of 0.5% bupivacaine 6.0 ml and fentanyl 100 micrograms given extradurally, followed by an infusion of 0.08% bupivacaine 15 ml h-1 plus fentanyl 37.5 micrograms h-1, with a loading dose of 0.5% bupivacaine 6.0 ml and saline 2.0 ml, followed by an extradural infusion of 0.08% bupivacaine alone, per hour. Analgesic levels were more consistent and sustained in mothers who received fentanyl in addition to bupivacaine, and the duration from the time of the loading dose to the first top-up was extended considerably in this group. The only significant side effect was a high incidence of mild pruritus in the fentanyl group. The addition of fentanyl to the extradural loading dose and subsequent infusion of local anaesthetic is a satisfactory alternative to giving higher doses of local anaesthetic alone.