The relative accuracy of Thermoscan PRO-1 (Thermoscan, USA), an infrared ear thermometer, in an unadjusted mode was examined in 21 patients under general anesthesia, using the esophageal and tympanic membrane temperatures as the reference values. The correlation coefficient between the temperature measured by Thermoscan PRO-1 and the esophageal temperature, and that between the temperature measured by Thermoscan PRO-1 and the tympanic membrane temperature, were 0.953 and 0.942, respectively (P < 0.01). The "limits of agreement" between the temperature measured by Thermoscan PRO-1 and esophageal temperature, and between the temperature measured by Thermoscan PRO-1 and tympanic membrane temperature, were -0.5-0.4 degrees C and -0.5-0.5 degrees C, respectively. We conclude that Thermoscan PRO-1 is sufficiently reliable for monitoring body temperature during surgery.