The most accurate method of obtaining body temperature is the core temperature. Traditionally, esophageal measurements have been used in anesthetic settings. A method to assure similar accuracy for conscious patients was needed. A group of 20 postoperative patients ranging in age from 60 to 95 years was studied. All had pulmonary artery catheters for perioperative and postoperative monitoring. For all 20 patients, temperatures measured through the pulmonary artery catheter were compared with temperatures measured with a tympanic thermometer. It was hypothesized that there was no significant difference between the two temperature measurements. Mean temperature measured was 37.2 degrees C in the control group (pulmonary artery temperatures) and 37.3 degrees C in the experimental group (tympanic membrane temperatures). Using the descriptive statistic and analysis of variance, the F statistic indicated that there was no significant difference between the two groups. The null hypothesis that there is no significant difference between temperatures measured with a tympanic membrane thermometer and pulmonary artery catheter was accepted.