SummaryWe have used the up-and-down allocation technique to assess the relative analgesic potencies of epidural ropivacaine alone and ropivacaine combined with sufentanil 0.75 mg.ml 21 in 42 women requesting epidural analgesia in the first stage of labour. Parturients were randomly allocated to one of the two epidural solutions in a double-blind manner. The concentration of local anaesthetic was determined by the response of the previous parturient: an effective concentration (pain # 10 mm on a 10-cm visual analogue pain score within 30 min) resulted in a 0.01% decrease in the concentration of ropivacaine for the next parturient, an ineffective concentration resulted in a 0.01% increase. Minimum local analgesic concentration of ropivacaine alone was 0.13% (95% CI 0.12±0.13%) compared with 0.09% (95% CI 0.08±0.1%) for ropivacaine with sufentanil (p , 0.00001).