OBJECTIVE: To determine whether abnormalities in lung mechanics detected in infants during the acute phase of meconium aspiration syndrome persist after treatment with extracorporeal membrane oxygenation (EMCO). DESIGN: Prospective, descriptive study. Prospective evaluation of airway function and lung mechanics during and after ECMO by pulmonary function testing at 1.8 +/- 0.5 days of EMCO (period 1), follow-up at 1.4 +/- 0.2 days (period 2), and 7.0 +/- 0.9 days (period 3) after decannulation from ECMO. SETTING: Tertiary care neonatal/pediatric ICU. PATIENTS: Twelve neonates undergoing ECMO treatment for severe meconium aspiration syndrome that was refractory to conventional mechanical ventilation. INTERVENTIONS: Maximum expiratory flow-volume curves were studied with the deflation flow-volume curve technique, and compliance and resistance of the respiratory system were studied with partial passive flow-volume curves. MEASUREMENTS AND MAIN RESULTS: Respiratory system compliance was the only index of respiratory mechanics that was significantly (p less than .05) improved (0.96 +/- 0.1 vs. 0.61 +/- 0.1 mL/cm H2O/kg) immediately after decannulation from ECMO compared with period 1. Clinically important (p less than .05) improvement in forced vital capacity (28.0 +/- 5.5 vs. 16.1 +/- 1.9 mL/kg), respiratory system compliance (1.01 +/- 0.2 vs. 0.61 +/- 0.1 mL/cm H2O/kg), and maximum expiratory flow at 25%/forced vital capacity (1.0 +/- 0.3 vs. 2.2 +/- 0.3) was evident only during period 3 compared with period 1. CONCLUSIONS: We conclude that improvements in the clinical condition and oxygenation, permitting successful decannulation from ECMO, are achieved before clinically important improvements in lung mechanics.