Perfusion scan of the lungs offers a new approach to the diagnosis of pulmonary disease. The technic to be reported here employs the intravenous administration of aggregates of I-tagged human serum albumin. The following is a report of the findings in 27 lung scan of various pulmonary disease. The results were as the following: 1. A reduction of pulmonary arterial blood flow was found in chronic inflammatory disease such as bronchiectasis and pulmonary tuberculosis. 2. In the acute pulmonary inflammatory disease suoh as pneumonia and lung abscess there was diminution of pulmonary arterial blood flow corresponding to the pathologic lesion. 3. A reduction of pulmonary arterial blood flow was also found in pleural effusion, pleural adhesion and fibrothorax. 4, In primary bronchogenic cancer and secondary lung cancer we found marked re6uction of pulmonary arterial blood flow corresponding to the cancer lesion. 5. Almost complete lack of pulmonary arterial blood flow in one side total lung was found in a patient with idiopathic unilateral hyperlucent lung.