In the past twenty-four months we have engaged in a program to encourage the performance of pulmonary angiography in suspected cases of life-threatening pulmonary embolism. Pulmonary embolectomy is performed with or without the aid of the heart lung bypass (1), following clipping (2) or ligation of the inferior vena cava in patients with occlusion of more than 60 per cent of the pulmonary arterial bed. Anticoagulant therapy, with or without inferior vena cava interruption, is administered to patients with lesser obstruction. If pulmonary embolism is excluded, appropriate studies are performed to establish the proper diagnosis, and indicated therapy is instituted. Treatment which may have been directed toward embolism is discontinued. The following cases illustrate the advantages of pulmonary angiography. Case I: A 50-year-old woman in critical condition with the diagnosis of pulmonary embolism was transferred from an outside hospital. Four weeks previously resection of a small bowel hemangioma had been pe...