The effects of cuirass-assisted ventilation have been studied in 25 subjects with chest wall disease. Cuirass respirators increase ventilation in proportion to the peak negative pressure within the cuirass shell and the respiratory rate. Positive pressure applied during expiration produces little additional ventilation. During cuirass-assisted ventilation end-expiratory volume increases, arterial carbon dioxide tension (PaCO2) falls and arterial oxygen tension (PaO2) rises. Cardiac output is unchanged. Paradoxical chest wall motion is corrected by cuirass-assisted ventilation and restriction of chest wall expansion by the cuirass shell is minimal. Jacket-type respirators can produce larger tidal volumes than the cuirass at the same peak negative pressure, but are associated with greater air leakage.