In a group of 30 baboons the left lung was extirpated and, after a waiting period of 1-3 hours, reimplanted. Postoperative roentgenograms at the end of 1 week showed a diffuse cloudiness throughout the lung, which resolved by the end of 4-6 weeks in the majority of cases. Pneumothorax, either ipsilateral, contralateral, or bilateral, was noted in 14 animals. Stenosis of the anastomosed bronchus developed in 3 animals. The incidence and cause of these findings are briefly discussed. The clinical applicability of pulmonary autotransplantation is described.