The success of lung volume reduction with endobronchial valves in patients with Chronic Obstructive Pulmonary Disease (COPD) depends on the absence of collateral ventilation into the target lung segment. Collateral ventilation can be assessed using time-resolved 3He MRI, but providing this clinical application with 129Xe MRI would be desirable. Two patients with severe COPD were scanned with time-resolved 3He and 129Xe MRI. In both patients, collateral ventilation visualised using 3He MRI was not observed with 129Xe MRI. Although the small sample size is a limitation, this suggests that 129Xe MRI may not be suitable for the assessment of collateral ventilation.