Nitrofurantoin is a widely prescribed antibiotic used for the treatment of urinary tract infections. In some patients it can produce an acute pulmonary reaction ranging from mild dyspnea to noncardiogenic pulmonary edema. Symptoms include fever, dyspnea, chills, cough, and chest pain. Physical examination generally reveals an acutely ill, extremely apprehensive patient in varying degrees of respiratory distress. Fever is usually present and there is an increase in heart rate and respiratory rate. Cyanosis, rales, and a maculopapular rash are common findings. Laboratory studies typically demonstrate a leukocytosis with eosinophilia, varying degrees of hypoxia and hypocapnia, and a mild to moderate elevation of the erythrocyte sedimentation rate. The chest x-ray study may be normal but more often demonstrates bilateral lower lobe interstitial infiltrates frequently accompanied by pleural effusions. Treatment in the majority of cases requires only stopping the drug, but steroids, bronchodilators, or antihistamines may be used in selected cases. Once the diagnosis is made and the drug withdrawn, prognosis for full recovery is excellent.