Gases of low solubility (e.g., NO/sub 2/) may not irritate upper respiratory tract but may act insidiously on lower tract producing edema and bronchiolitis. Cases of bronchiolitis (1 resulting in death) from exposure to brown nitrous fumes are reported. There were no or slight symptoms at first but severe ones after about 1 wk. Pathology appears as acute pulmonary edema with damage and desquamation of alveolar epithelium particularly and that of respiratory bronchioles somewhat. Patchy atelectasis, bronchopneumonia and disruption of fibers in cell walls may also occur. Severe cases have obliteration of lumen (bronchiolitis obliterans) with extreme distress and death.