6 autopsy lungs with interstitial pulmonary fibrosis were subjected to comparative angiographical and morphological investigations of bronchial arteries. During the final stage of interstitial pulmonary fibrosis, bronchial arteries were increased in number, and so were their anastomoses with pulmonary arteries. Extensive formation of broncho-pulmoary anastomosis as well as proliferation and formation of new bronchial arteries, is associated with interstitial chronic inflammation and fibrosis in the lung. The findings explain functional interconnections between the vessels of the systemic and the pulmonary circulations by direct artery-to-artery anastomoses, with a negative influence on pulmonary hypertension.