A high-frequency oscillator ventilator has a first gas conduit with an opening for gas connection with a patient's airways and a bias gas flow inlet and a bias flow outlet disposed to define therebetween a flow path for a bias gas within the first conduit. An oscillator operable to alternately introduce a volume of additional gas from a source into, and to withdraw at least the same volume of gas from, the first gas conduit, thereby inducing pressure oscillations in gas within the first conduit to move gas along a path intersecting the flow path for a bias gas alternately into and out of the opening at a predetermined high-frequency dependent on the output of a control signal generator.