Ventilatory work of breathing is defined as a variable referring to the mechanics of the breathing function of the lung, ascertainable from the alveolar pressure-breathing volume diagram. Information on the resistance of the respiratory canal can be obtained. The ventilatory respiration of 93 healthy persons at spontaneous resting breath frequency (15 ± 3 min) was investigated, with the aid of a body plethysmograph. A mean value of 2.21 g·cm/ml (s = 0.92) was obtained. A dependence on age and sex could not be statistically proved. The value of 4.0 g•cm/ml (= 2 s) is discussed as a limit to a pathological increase. With a rise in breath volume, relative weight and also, marginally, the spontaneous resting breath frequency, a significant increase of ventilatory work of breathing in normal persons must be anticipated. A so-called index of ventilatory work of breathing (breath volume/alveolar pressure changes under defined conditions) correlates significantly with ventilatory work of breathing and can thus be regarded as an orientating value for the resistance of the respiratory canal. Its mean value amounts to 3.10 cm/cm, with a SD of 1