At various times after clinical embolism, bronchial arteriography was performed in 23 patients with documented pulmonary embolism. In 17 patients with no radiologic infiltrates, chronic stage bronchial arteriograms demonstrated bronchial-to-pulmonary arterial collaterals with antegrade filling of distal pulmonary arteries. No collateral circulation was detected at the acute stage. In one case of massive pulmonary embolism with well-developed bronchial-to-pulmonary arterial collaterals and antegrade filling of distal pulmonary arteries, brisk back-bleeding occurred at surgery, and an excellent therapeutic result following thromboembolectomy was gained. By contrast, in six patients with radiologic infiltrates, only one patient (subacute stage) showed bronchial-to-pulmonary arterial collaterals; these were peripheral and associated with retrograde, not antegrade, filling of distal pulmonary arteries. Bronchial arteriography has provided information about the development of collateral circulation in pulmonary embolism, and might be useful when thromboembolectomy is planned.