Six anesthetized paralyzed cats with normal lungs were ventilated by high-frequency chest wall compression (HFCWC) at 5 Hz using a single-chamber circumferential cuff enclosing the thorax from the axillae to the xiphisternum. PaCO2 during HFCWC + PEEP (3 cm H2O) was significantly (p less than .0005) lower compared with conventional mechanical ventilation (CMV). End-expiratory lung volume (VL) during HFCWC + PEEP was significantly (p less than .001) lower than VL during CMV + PEEP but was higher than VL during CMV without PEEP. After the cats' lungs were stiffened by repeated saline lavage, CMV + PEEP at a mean airway pressure (Paw) of 10 cm H2O was compared with HFCWC + continuous positive airway pressure (CPAP) at an equal or lower Paw. A significant decrease in PaCO2 (p less than .02) during HFCWC occurred but no significant differences were observed in PaO2, VL, or compliance. Arterial BP and cardiac output were similar between CMV + PEEP and HFCWC + CPAP. In cats with normal lungs, VL can be maintained by applying CPAP during HFCWC, and in those with injured lungs, HFCWC + CPAP produces comparable gas exchange at a Paw equal to or lower than that used during CMV + PEEP.