Although suppression of thermoregulatory mechanisms during anaesthesia is generally assumed, the extent to which thermoregulation may be inactive is unknown. Twenty unpremedicated, ASA physical status class I patients (17 men and 3 women) scheduled for retinal detachment surgery were studied to evaluate the different changes of core and two skin-surface temperatures during halothane or isoflurane anaesthesia. Anaesthesia was induced by mask inhalation of halothane or isoflurane in nitrous oxide 70% and oxygen and was maintained by mechanical ventilation during surgery with halothane or isoflurane in nitrous oxide 50% and oxygen only. Core temperature (rectus) and skin-surface temperatures (forearm and fingertip) were measured during surgery using three separate thermometers (Y.S.I.: Yellow springs instrument Co., Inc. G541-211-Y01-33A0). Operating room temperatures were recorded in every case. Significant vasoconstriction was prospectively defined by a skin-surface temperature gradient between two sampling sites > or = 4 degrees C. The result indicated that there was no significant difference between core temperatures and skin-surface temperature gradients during halothane anaesthesia and isoflurane anaesthesia. However, three of the ten patients had their skin-surface temperature gradients > or = 4 degrees C in the halothane group. None of the ten patients had their skin-surface temperature gradients > or = 4 degrees C in the isoflurane group.