Pulmonary embolism often is undetected during life, even though adequate diagnostic procedures are available, probably because the condition is not suspected. Chest radiographs were reviewed for changes in the right descending pulmonary artery in 73 patients with confirmed pulmonary embolism and in 85 in whom the original suspicion subsequently was not confirmed. In embolic patients, the vessel, measured at four different levels starting from the superior venous angle, was larger during acute embolization than some weeks later. In particular, the two proximal diameters of descending pulmonary artery were significantly enlarged (p less than 0.01). This enlargement of the superior part was responsible for the shape modification of the vessel, which appeared to taper off sharply. Some weeks later, the artery took back its regular cone shape, tapering gently. In about one-fourth of the patients with pulmonary embolism, enlargement and shape modification were so marked that the artery showed a special "sausage" appearance. This feature did not occur in patients with unconfirmed suspicion of pulmonary embolism. Recognition of enlargement of the descending pulmonary artery may increase suspicion of pulmonary embolism; in particular, detection of "sausage" appearance of the vessel should identify patients with high probability of disease.