The effects of the ventilatory patterns of a conventional ventilator (SV-900) and a low-compression ventilator (system H) were studied in 12 patients with respiratory failure (RF). Volume-controlled ventilation at frequencies (f) of 20 breath/min (SV-20) with SV-900, and 20 (H-20) and 60 (H-60 = high-frequency positive-pressure ventilation, HFPPV) breath/min with system H was given. Inspiration constituted 25% (with an inspiratory pause of 10%) of the ventilatory cycle with SV-900 and 22% with system H. Intratracheal (ITP), intrapleural, systemic and pulmonary arterial (PAP), and central venous (CVP) pressures were measured at normoventilation. During H-60, normoventilation was provided with smaller tidal volumes and lower mean intratracheal pressures than during SV-20 and H-20. Cardiac index and oxygen transport were not affected by changes in ventilatory pattern. The respiration-synchronous variations in CVP, PAP, and pulmonary capillary wedge pressure (WP) during ventilation at 20 breath/min were abolished during HFPPV. In the most severely ill patients, long-term HFPPV was uneventful. Airway suctioning during ventilation with oxygen was an important feature of the pneumatic valve principle (system H). The results of this study indicate that volume-controlled HFPPV is as efficient and as well accepted by the patient as conventional ventilation (SV-20).