Our investigations have demonstrated that the effect of oscillatory high-frequency ventilation (HFO) on gas exchange in dogs is directly proportional to the oscillatory flow amplitude VM. Because of the equation: VM = PM/Z, gas exchange is increasing with rising oscillatory amplitude of the ventilation pressure PM and decreasing with rising impedance Z of the respiratory system. This system consists of endotracheal tube and the lungs of the dog investigated. The impedance Z = square root of R2 + X2 (resistance R and reactance X) achieves a minimal value near at the resonant frequency (reactance X = 0, in healthy intubated dogs near at 5 Hz) and increases with rising oscillatory frequency. Thus the oscillatory high-frequency ventilation is most effective near to the resonant frequency of the respiratory system. The results presented allow the conclusion that the application of high-frequency ventilation can be optimized by monitoring the respiratory mechanics parameters.