An 82-year-old woman was admitted to the hospital with progressive dyspnea and hypoxemia. She had a history of mild asthma and had never been hospitalized. One month prior to admission, a new primary care physician recommended that she try montelukast. Two weeks later, she developed a dry nocturnal cough that progressed to dyspnea at rest and orthopnea. She denied fever or chills. There were no other recent changes in her medications.