Serial radiographic examinations were used to assess the incidence of bilateral and unilateral pneumothorax and its resolution following the introduction of air into a pleural space in each of 24 adult mix-breed dogs. Twenty-two (92%) dogs developed bilateral pneumothorax and two dogs (8%) developed unilateral pneumothorax. Volumes of air equal to 5 ml/kg, 15 ml/kg, and 45 ml/kg of body weight had resolved in all dogs developing bilateral pneumothorax by 7, 10, and 14 days, respectively. The vertical beam left lateral recumhent and the expiratory horizontal beam ventrodorsal views were the most effective radiographic views for the detection of pneumothorax. Separation of the visceral and parietal pleural surfaces on the horizontal beam ventrodorsal view was a better indication of small amounts of air in the pleural spaces than separation of the heart from the sternum on the vertical beam lateral view. The right lateral recumbent view, regardless of heam orientation, was most sensitive for the detection of differences in the amount of air in the pleural spaces.