Recurrent pulmonary emboli ultimately may produce respiratory insufficiency, severe hypoxemia, and progressive pulmonary hypertension. In many patients this syndrome is silent in its initial phases, and when thrombophlebitis is present it is often unresponsive to anticoagulant therapy. Unless pulmonary embolectomy is undertaken, most of these patients characteristically succumb with severe respiratory insufficiency. Twenty-five patients with this syndrome have been evaluated at the Duke University Medical Center, and 14 were selected for elective pulmonary embolectomy for relief of severe and incapacitating pulmonary insufficiency. In each patient preoperative pulmonary scans and arteriography demonstrated a high degree of vascular occlusion. The obstructing lesions affected both lungs in the majority of patients. Bronchial arteriography was found to be a very valuable method for demonstrating patency of the pulmonary arteries distal to occluding lesions by retrograde filling through collateral vessels joining the bronchial and pulmonary circulations. Preoperatively radionuclide angiocardiography revealed severe right ventricular dysfunction with significantly depressed ejection fractions at rest and during exercise. Retrograde pulmonary arterial flow as shown by selective bronchial arteriography was excellent in ten patients, fair in three, and absent in one. Long term follow-up indicated a clear relationship between the magnitude of arterial backflow at the time of embolectomy and the degree of clinical improvement. There were two perioperative deaths, one from massive reperfusion pulmonary hemorrhage and another from intractable right ventricular failure. Eleven patients with this syndrome were unsuitable candidates for embolectomy and of these, nine had severe distal emboli diffusely spread in the small pulmonary arteries and not amenable to direct removal. One patient had severe right ventricular failure with extreme pulmonary hypertension (145/45 mmHg) and another was massively obese with severe congestive heart failure and expired in the hospital a week later. In this group of 11 patients, three succumbed and most of the others are currently totally debilitated at rest (NYHA Class IV). Long-term follow-up of the surgically managed patients (1 to 15 years) shows that ten patients improved from NYHA functional Class IV to either I or II, another patient from Class III to Class I, and a final patient was only minimally improved.(ABSTRACT TRUNCATED AT 400 WORDS)