Evidence for severe intrapulmonary bleeding was obtained in 3 anticoagulated patients who presented with pulmonary infiltrates. The diagnosis of pulmonary hemorrhage was based on findings of markedly elevated quantities of stainable hemosiderin and hemoglobin in alveolar macrophages retrieved by bronchopulmonary lavage. In 2 of the patients, roentgenographic abnormalities regressed after anticoagulation was reversed. The third patient died and massive bilateral pulmonary hemorrhage was found at autopsy. The syndrome of occult pulmonary hemorrhage was characterized clinically by dyspnea, unexplained acute anemia, and infiltrates with an alveolar pattern on chest roentgenogram. Hemoptysis was conspicuously absent. Bronchopulmonary lavage and quantification of alveolar macrophage hemosiderin content may be useful in identifying intrapulmonary bleeding occurring in an otherwise occult manner. Recognition of pulmonary hemorrage in anticoagulated patients is important because reversal of anticoagulation can be life saving.