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This open, multicentre study compared the efficacy and safety of remifentanil with fentanyl during balanced anaesthesia with 0.8% isoflurane (end-tidal concentration) for major abdominal and gynaecological surgery, and the efficacy and safety of remifentanil for pain management in the immediate postoperative period.Two-hundred and eighty-six patients were randomized to receive remifentanil 1 μg kg–1 followed by 0.2 μg kg–1 min–1 (n =98), remifentanil 2 μg kg–1 followed by 0.4 μg kg–1 min–1 (n =91) or fentanyl 3 μg kg–1 (n =97) at induction. Thereafter, the study opioids and isoflurane were titrated to effect during the operation.Compared with fentanyl, remifentanil 2 μg kg–1 followed by 0.4 μg kg –1 min–1 reduced the incidence of response to tracheal intubation (30% vs. 13%, P < 0.01), skin incision (33% vs. 4%, P < 0.001) and skin closure (11% vs. 3%, P < 0.05), respectively. Patients receiving remifentanil 1 μg kg–1 followed by 0.2 μg kg –1 min–1 had fewer responses to skin incision than the fentanyl group (12% vs. 33%, P < 0.001), but the incidences of response to tracheal intubation and skin closure were similar. Significantly fewer patients in both remifentanil groups had ≥ 1 responses to surgical stress intraoperatively compared with fentanyl (68% and 48% vs. 87%, P < 0.003). The mean isoflurane concentrations required were less in both remifentanil groups compared with the fentanyl group (0.1%, P =0.05). In remifentanil-treated patients, continuation of the infusion at 0.1 μg kg–1 min–1 with titration increments of ± 0.025 μg kg–1 min–1 was effective for the management of immediate postoperative pain prior to transfer to morphine analgesia. However, a high proportion of patients experienced at least moderate pain whilst the titration took place.Anaesthesia combining isoflurane with a continuous infusion of remifentanil was significantly more effective than fentanyl at blunting responses to surgical stimuli. Significantly fewer patients responded to tracheal intubation with remifentanil at 0.4 μg kg–1 min–1, supporting the use of a higher initial infusion rate before intubation. Both remifentanil and fentanyl were well-tolerated, with reported adverse events typical of μ-opioid agonists.