Lung biopsy and autopsy specimens of 12 patients with amiodarone pulmonary toxicity were studied to better characterize the pathology of amiodarone lung. For comparison, the autopsy specimens of five patients taking amiodarone without pulmonary side effects also were examined. Interstitial pneumonia was the most common manifestation of amiodarone lung and was characterized by interstitial inflammation, fibrosis, and hyperplasia of type II pneumocytes. Hyaline membranes were present in two cases. Foamy alveolar macrophages were present in all but one patient, and in four associated organizing pneumonia was present. Foamy alveolar macrophages also were present in three of five clinically nontoxic patients. Electron microscopy demonstrated membrane-bound lamellar inclusions in all of the three cases of amiodarone lung examined. Inclusions also were present in two of five patients who died of other causes. The authors conclude that amiodarone lung is primarily an interstitial pneumonia. Foamy alveolar macrophages and cytoplasmic lamellar inclusions are characteristic, but neither is specific, and their presence alone does not distinguish toxic from nontoxic patients.