One hundred and one women (ASA grades I and II) were anaesthetized for routine gynaecological surgery using an intravenous (i.v.) anaesthetic technique combining propofol and alfentanil. The patients were allocated randomly into groups. Group one received 33% oxygen in nitrous oxide and group two received 33% oxygen in air (total i.v. anaesthesia). The group receiving nitrous oxide required significantly less (P < 0.05) of the propofol and alfentanil mixture to maintain anaesthesia and this was found to reduce the mean cost of anaesthesia by £1.70, (P < 0.05). There was no significant difference in the incidence of post-operative complications between the two groups. We suggest that nitrous oxide may be used to reduce the cost of total i.v. anesthesia with propofol and alfentanil without causing any increase in post-operative morbidity in patients undergoing routine gynaecological surgery.