We assessed the short-term effect of steroids on respiratory mechanics in eight mechanically ventilated patients with chronic airflow obstruction (CAO) and hypercapnic respiratory failure. Airflow (V), airway pressure (Paw), and changes in pulmonary volume were measured using a conventional ventilator. End-expiratory and end-inspiratory airway occlusions were performed to assess intrinsic PEEP (PEEPi), static compliance of total respiratory system (Cstrs), maximum inspiratory resistance (Rrsmax), and minimum inspiratory resistance (Rrsmin). These parameters were recorded at control, 30 min after saline, and 90 min after steroid (methylprednisolone 0.8 mg/kg intravenous) administration. No significant changes were found in respiratory mechanics after administration of saline. Steroids induced a significant decrease (p < 0.01) in inspiratory resistance (Rrsmax from 20.3 +/- 8.6 cm H2O/L/s (control) to 15.3 +/- 6.1 (90 min) and Rrsmin from 16.2 +/- 8.0 (control) to 11.9 +/- 6.5 (90 min), with no significant reduction in Paw and Cstrs. The PEEPi, reflecting pulmonary dynamic hyperinflation, was also significantly reduced (-16% from control). We conclude that in mechanically ventilated CAO patients, steroids may be useful in improving respiratory mechanics and therefore in providing better conditions for weaning from mechanical ventilation.