Eight patients with severe emphysema entered a pilot study of unilateral volume reduction by endobronchial valve insertion. Five patients had emphysema judged too severe for volume reduction surgery and three refused the operation. After valve insertions, the median forced expiratory volume in 1 s (FEV1) increased from 0.79 L (range 0.61-1.07) to 1.06 L (0.75-1.22) (difference 34%, p=0.028) and the median diffusing capacity (TL(CO)) increased from 3.05 mL/min/mm Hg (2.35-4.71) to 3.92 mL/min/mm Hg (2.89-5.40) (difference 29%, p=0.017). CT scans showed a substantial reduction in regional volume in four of the eight patients. Two patients developed a transient pneumothorax (one requiring drainage) but we recorded no other important adverse effects during follow-up. Lung-volume reduction can be achieved with unilateral bronchoscopically placed valve implants in patients with severe emphysema with acceptable short-term safety and worthwhile functional benefits.