Oesophageal temperature was recorded after induction of anesthesia, and further, at one, two and three hours. Temperature in the operation hall was continuously monitored. In relation to the temperature in the operating hall the effects on the patient were of three kinds: 1. operating halls with low temperatures (under 21 degrees C) where all the patients become hypothermic; 2. operating halls with an intermediate temperature (21-24 degrees C), where 67% of the patients remain normothermic; 3. operating halls with high temperatures (above 24 degrees C) where all the patients remain normothermic, although these temperatures are uncomfortable for the medical personnel, and increase the septic risk of the patient. When the oesophageal temperature of the patients falls by 0.5 degrees C chills will occur in 40% of the patients. Thermal falls of less than 0.5 degrees C will also determine chills but in only 10.5% of the cases. Immediate postanesthesia chills are also recorded in normothermic patients, but there is a direct relationship between the temperature in the operating hall, the degree of hypothermia and the frequency of chills, while the site of the surgery or the duration of the operation have but an unsignificant influence on intra-anesthetic temperature.