The mechanism by which tracheobronchial arterial supply is reconstituted following heart-lung transplantation was investigated in seven monkeys (3 allografts, 2 autografts, and 2 nontransplanted control monkeys) and three patients. Descending tracheal branches of the thyrocervical arteries provided the major tracheal vascular supply. A collateral branch arising from atrial branches of the left coronary artery supplied tracheobronchial branches in the region of the carina in one allograft. In the three patients studied to date by coronary arteriography, a similar collateral supply to the region of the carina and proximal bronchi was demonstrated from atrial branches of both the left and right coronary circulation.