We measured gastric emptying (by paracetamol absorption) and duration of analgesia in 30 women in labour after extradural injection of 0.375% bupivacaine 10 ml either alone or combined with fentanyl 100 micrograms. Treatment was administered double blind by random allocation after the first request for analgesia. The median (range) times to maximal serum concentration of paracetamol were 60 (15-90) min and 75 (30-180) min after administration in the control and fentanyl groups, respectively (P = 0.026), and corresponding mean (95% confidence interval) maximal concentrations of paracetamol were 27.3 (18.8-35.8) micrograms ml-1 and 18.0 (15.1-20.9) micrograms ml-1 (P = 0.020). Mean duration of analgesia, from the first extradural bolus until return of pain in those given bupivacaine alone was 113 (87-139) min and 154 (131-176) min when fentanyl was added to the local anaesthetic (P = 0.016). These results confirm the prolongation of analgesia after fentanyl supplementation of lumbar extradural analgesia, but indicate that it results in delayed gastric emptying.