Air leak is a major contributor to increased length of stay and postoperative morbidity following pulmonary surgery. The effectiveness of a new photopolymerized synthetic hydrogel (FocalSeal, Focal, Inc., Lexington, MA) as a sealant for pulmonary air leaks was determined in 10 mongrel dogs (20-35 kg). The animals were anesthetized and underwent left-sided anterolateral thoracotomy with amputation of a 2 x 3-cm segment of the lung apex. Hemostasis was achieved and terminal bronchial openings of 1.5 to 3 mm with vigorous air leaks were identified. After successful injury, the dogs were randomly assigned to sealant (n = 5) or control (n = 5) groups. In treated animals, the sealant was applied by brushing the solution to the cut parenchymal surface and solidified while briefly interrupting ventilation (40-60 seconds) using visible illumination (450-550 nm) from a xenon light source. Controls received no sealant. A single chest tube was maintained at the injury site with a continuous negative pressure of 20 cm of water. All dogs were extubated and allowed to breathe spontaneously under sedation for 24 hours. Chest radiographs were taken postsurgery and presacrifice. All control animals (n = 5) showed persistent vigorous air leak for the duration of the 24-hour observation period. All treated air leaks resolved immediately, and four of five remained sealed throughout the observation period. One leak reappeared after 17 hours due to inadequate sealant thickness over a 3-mm terminal bronchus. Gross evaluation of the treatment group at the end of 24 hours demonstrated intact sealant well adherent to the parenchyma. No evidence of atelectasis or excessive edema was seen, and no sealant-related complications or toxic effects were noted. Radiologically, lungs were fully inflated. Histologic evaluation at 24 hours revealed no evidence of a strong cellular response to the synthetic sealant, and no fibrosis or adhesions were seen, the onset of the healing process was favorable, indicating good biocompatability. In conclusion, this material was found to be an effective means for sealing bronchial and parenchymal air leaks in this model and warrants clinical evaluation.