The present study is a continuation of experimental efforts to evaluate the suitability of various graft materials for pulmonary arterial replacement. The clinical indications for pulmonary artery replacement and bypass, including trauma and segmental arterial occlusion, and the literature relating to experimental pulmonary artery replacement have been discussed in detail elsewhere.2 Material and Methods Healthy mongrel dogs were used. The weight of the dogs generally was in the 8 to 12 kg. range. Intravenous thiopental (Pentothal) was utilized for anesthesia. Oxygen was administered through an endotracheal tube by means of a mechanical respirator. The left chest was entered through a fourth intercostal space incision. A 3 to 4 cm. segment of proximal left subclavian artery was isolated and resected after proximal and distal arterial ligation. The left pulmonary artery, the main pulmonary artery, and the proximal segment of the right pulmonary artery were dissected free of pericardium and surrounding