In a prospective comparative study 240 patients received extradural bupivacaine, either by regular timed injections or "on demand", for pain relief during the first stage of labour. Three concentrations of bupivacaine were used (0.5%, 0.375% and 0.25%). Quality and continuity of analgesia, motor blockade, spread of sensory blockade, cardiovascular changes, fetal outcome and maternal sequelae were recorded. Overall, the analgesia provided by regular top-up injections was superior to the on demand technique, especially when 0.375% bupivacaine was used. This improved analgesia was achieved without causing an increased incidence of operative deliveries or deleterious sequelae, with respect to the mother or the neonate.