Exposure to the toxic gases carbon monoxide and nitrogen dioxide (NO2) in indoor ice arenas occasionally occurs and may result in severe symptoms. The gases are produced by ice resurfacing machines operating on hydrocarbons, and in certain conditions toxic levels accumulate. The damage to lung tissues caused by NO2 may not be evident until after a latency time of 1/2-2 days. The role of corticosteroids in the treatment is controversial, but there are clinical experiences as well as experimental data supporting their use. We report two cases of toxic pneumonitis, with delayed onset, due to NO2 exposure during an ice hockey game in an indoor arena. Signs and symptoms were cough, dyspnoea, haemoptysis, hypoxaemia and reduced peak expiratory flow. Chest radiographs showed parenchymatous infiltrative lesions and alveolar consolidation. Both patients were treated with high doses of corticosteroids by inhalation and orally or intravenously. Their condition rapidly improved and pulmonary function was restored.