This study tested the hypothesis that high dose systemic alfentanil administered before and during abdominal hysterectomy would pre-empt post-operative pain to a greater extent than administration of either low dose alfentanil or no alfentanil perioperatively. Patients (ASA 1 or 2) were randomly assigned to group 1 (n = 15), no opioid; group 2 (n = 15), low dose alfentanil; or group 3 (n = 15), high dose alfentanil. Anaesthesia was induced in group 1 with midazolam and thiopentone and was maintained with isoflurane and 70% N2O in O2. Anaesthesia was induced in group 2 with midazolam, thiopentone and i.v. alfentanil (30 microg kg(-1)), and was maintained with isoflurane, 70% N2O in O2, and bolus doses of i.v. alfentanil (10-20 microg kg(-1)) every hour. Anaesthesia was induced in group 3 with midazolam and i.v. alfentanil (100 microg kg(-1)), and was maintained with 70% N2O in O2, and an infusion of i.v. alfentanil (1-2 microg kg(-1) min(-1)). Blood samples were drawn at 30 and 120 min after surgery and assayed for plasma alfentanil. Morphine consumption and VAS pain scores were consistently lowest in group 3 over the 48 h study period. A composite measure of pain and morphine consumption was significantly lower in group 3 than group 2 up to 6 h after surgery, and significantly lower than group 1 up to 12 h. No adverse effects were observed. A 6-month follow-up did not reveal any significant differences among the three groups. It is concluded that intra-operative high dose alfentanil anaesthetic pre-empts post-operative pain after abdominal hysterectomy, but the effects are small and of short duration. Surgical procedures carried out under general anaesthesia using standard (and even high) doses of opioids intraoperatively provide suboptimal protection from the injury barrage brought about by incision and subsequent noxious surgical events.