Five hundred and seventeen women in labour receiving extradural analgesia, using bupivacaine plain solution, were randomly allocated to one of three groups. Group A received 6–8 ml of 0.5% solution, group B 10–14 ml of 0.25% solution, and group C 6–8 ml of 0.25% solution. Spontaneous delivery occurred in 31.7% of patients in group A, 38.7% in group B and 53% in group C (P<0.001). The percentage of rotational forceps, ventouse and Caesarean section deliveries was similar in the three groups. Analgesia was most effective in group A, and least in group C, both during labour and at delivery, although assessment by linear analogue score suggested that the differences between the three groups were slight. Motor block was most frequent and rapidly progressive in groups A, but was progressive in all groups, and after five or more top-up injections, was similar in the three groups. Difficulties with micturition following delivery were significantly more common in group A.