We determined the time course of bronchial blood flow alterations after pulmonary microembolization. Embolization was induced by injecting 100-micrometers-diam glass beads into the right atrium so as to increase pulmonary arterial pressure from 13.8 +/- 1.8 to 35.7 +/- 2.6 Torr in 14 dogs. The increase in pulmonary vascular resistance averaged threefold after embolization (PE). The bronchial blood flow (Qb) was measured using the reference sample method with the 15 +/- 5-micrometers-diam labeled microspheres injected into the left atrium. Simultaneous blood reference samples were collected at constant rates from a femoral artery and the pulmonary artery. The pulmonary arterial reference sample was used to quantify the contribution of peripheral arteriovenous shunts to the total pulmonary activity, and the femoral arterial reference blood was used to quantify Qb. The Qb was decreased to one-third of its base-line value at 60-min PE (P less than 0.05) but not at 5 min PE. Qb was increased 300% at 2 wk PE. The decrease in flow was associated with an increased bronchovascular resistance, whereas the increase in flow was associated with a decreased resistance. The decrease in Qb at 60 min PE may be due to release of peripheral vasoconstrictor substances associated with pulmonary embolism. The finding that bronchial perfusion increased gradually after pulmonary vascular obstruction suggests that increased flow is due to neovascularization.