The 133Xe ventilation (V) studies, 99mTc perfusion (P) lung images, and pulmonary angiograms of 83 patients with obstructive pulmonary disease (OPD) and suspected pulmonary emboli (PE) were reviewed. Each patient had ventilation abnormalities suggesting OPD and at least one region showing matched V-P abnormalities. All angiograms were obtained within 72 hours of the V-P study and were reviewed independently. The overall sensitivity of V-P imaging for PE in this population was 0.83 and its specificity was 0.92. False-negative interpretations occurred in three of the 16 patients who showed ventilation abnormalities in more than 50% of their lung fields. In the 67 patients with ventilation abnormalities in less than or equal to 50% of their lung fields the sensitivity (0.95) and specificity (0.94) for detecting PE were high, V-P imaging is a reliable method for detecting PE in patients with regions of V-P match, if the ventilation abnormalities are limited in extent.