Fentanyl by continuous i.v. infusion (1.5 μg kg−1 min−1 or 0.5 μg kg−1 min−1) was compared with placebo infusion as an analgesic regimen for 24 h after hysterectomy. The drugs were infused using a new disposable device which required no external power source. All patients were allowed morphine i.m. if they experienced pain. Patients in the higher dose fentanyl group demanded less i.m. morphine and had better pain relief after operation, without important respiratory depression.