Lung transplantation has become a therapeutic option for end-stage pulmonary diseases, but after transplantation, infections and obliterative bronchiolitis (OB) are major causes of long-term morbidity and mortality. OB is a fibroproliferative disease, of poorly understood etiology, characterized by an irreversible decline in allograft function. Because diseases with tissue iron overload are characterized by fibrosis and end-organ failure, we studied the iron concentrations in BAL fluid and lung tissue in 10 lung allograft patients. BAL fluid revealed significantly elevated iron concentrations in allograft patients compared with five normal volunteers (135±16.54 µmol/L vs 33.65±7.48 µmol/L, respectively). Prussian blue staining of biopsy specimens of lung allograft tissue revealed an accumulation of iron primarily in alveolar macrophages. Immunohistochemical stains for ferritin revealed accumulation of the protein in macrophages, interstitium, vascular walls, and bronchiolar epithelium. Iron studies of the blood (serum ferritin and iron concentrations) revealed no evidence for systemic iron overload. In conclusion, patients with pulmonary allografts appear to have elevated concentrations of iron in lung tissue. This iron overload may place the allografts at increased risk of metal-mediated injury and fibrosis.