Temperature changes during general anesthesia were studied in relation to age, the duration and type of operative procedure(gastrectomy versus tympanoplasty) and the type of anesthetic(halothane versus conflurane) in 41 patients undergoing surgery in our centrally air-conditioned operating room. Body temperatures were recorded every 15 minutes after intubation by measuring the esophageal temperature in adults and the nasopharyngeal temperature in children. A comparison of temperature changes between adults and children showed a significant temperature decreases in adults during general anesthesia(-0.6 degrees C, p<0.001), while the temperatures of children remained stable. Comparisons of gastrectomy versus tympanoplasty groups indicated the operative site had little effect on the patient's body temperature. Patients who underwent a gastrectomy showed an average fall in esophageal temperature of 0.8 degrees C, where as there was an average temperature decline of 0.5 degrees C in tympanoplasty. Body temperature decrease was dependent on the duration of the operative procedure. The longer the procedure, the greater change in temperature. There was no significant difference between the effects of the volatile anesthetic agents on patient's body temperatures.