In a method for determining the exhaust gas temperature, the internal resistance of a lambda sensor is measured, and it is determined whether lean or rich mixture is present. Depending on which mixture type is present, the exhaust gas temperature associated with the measured internal resistance value is read out from one of two internal resistance value/exhaust gas temperature characteristic curves. This method can be used correspondingly for determining the sensor temperature from the internal resistance.The exhaust gas temperature determined as above only applies accurately for steady-state cases. In order to obtain satisfactory values even in non-steady-state cases, the exhaust gas temperature is averaged in a sliding manner. The present exhaust gas temperature is determined from the particular average value and the particular rise in the exhaust gas temperature/time curve.The mentioned methods permit the exhaust gas temperature to be determined without a separate temperature measuring element. With a single measurement, namely that of the internal resistance, the sensor temperature and the exhaust gas temperature can be determined with a high degree of accuracy.