The vaporization rates of enflurane were measured in 412 anaesthetics using appropriate fresh gas flow rates in Bain (12 litre min-1), Magill (6 litre min-1) and circle systems (3 litre min-1, 1 litre min-1 and "closed"). In all patients reducing the fresh gas flow rate resulted in lower enflurane consumption. The percent savings were 18-86% depending on the initial fresh gas flow rate and the size of the change in fresh gas flow. The reduction in enflurane use was more marked in inpatients (long cases) than in day-case patients (short cases).