A 5 year old male with no significant past medical history was admitted for respiratory distress with coughing beginning 2 weeks previously. On admission he was tachypneic and his oxygen saturation was 82% by pulse oximetry. Chest radiograph showed right and left lower lobe atelectasis. Differential diagnoses of his hypoxia included the new onset of reactive airway disease and pneumonia. During the 8 days since his admission, he received steroids, antibiotics and aminophylline. He continued to require oxygen. Radiographically, his left lung improved but the right lower lobe atelectasis worsened.