Nineteen critically ill patients with acute respiratory failure were studied to compare the hemodynamic effects of continuous positive-pressure ventilation (CPPV) and high-frequency jet ventilation (HFJV) at comparable levels of alveolar ventilation. Patients were divided into three groups: Group 1 included seven patients without circulatory shock in whom mean airway pressure (Paw) was slightly higher during CPPV than during HFJV (17.3 ± 3.0vs.13.0 ± 2.9 mm Hg); Group 2 included six patìents without circulatory shock in whom HFJV and CPPV were compared at the same level of Paw (19.2 ± 5.0 mm Hg); Group 3 included seven patients with circulatory shock in whom HFJV and CPPV were compared at the same level of Paw (16.0 ± 3.9 mm Hg). The following respiratory frequencies were used in HFJV: Group 1, 200 ± beats/min; Group 2, 238 ± 103 beats/min; Group 3, 286 ± 149 beats/min. In all patients comparable levels of Paco2were obtained with CPPV and HFJV. In Group 1 patients, mean arterial pressure, cardiac index, and stroke index were significantly higher during HFJV. In Group 2 patients, no significant difference was found between HFJV and CPPV. In Group 3 patients, the following hemodynamic variables were significantly higher during HFJV: mean arterial pressure (71 ± 24vs.84 ± 23 mm Hg), cardiac index (3.6 ± 1vs.4.1 ± 1.41 · min−1· m−2), and oxygen delivery (403 ± 93vs.471 ± 124 ml · m−1· m−2). However, Pao2was significantly lower (210 ± 105vs.155 ± 99 mm Hg, fractional inspired oxygen content [FIo2] 1) and pulmonary shunt (Qs/Qt) was significantly higher (31 ± 12vs.36 ± 11%) during HFJV. These results demonstrate that patients with circulatory shock and acute respiratory failure have a more favorable hemodynamic profile during HFJV than during CPPV at identical levels of Paw.