To evaluate the re-establishment of the bronchial circulation in lung transplantation, we studied 10 immunosuppressed dogs up to 14 weeks after left lung allografting. Selective in vivo bronchial arteriograms were performed repetitively via the transfemoral route. In the early postoperative period, no fillinf og vessels distal of the bronchial anastomosis could be shown. After 12 days, however, continuity of the bronchial arteries across the anastomosis was present, and dye-filled ramifications of these vessels were visualized on the secondary and tertiary bronchi. Reconstitution of the bronchial circulation was also confirmed by postmortem studies after injecting the isolated descending thorasis aorta with colored radiopaque material (microfil). The bronchial mucosa at autopsy was examined microscopically. There was no correlation between its viability and bronchial artery regeneration. Although early ischemia of the transplant bronchus may be after a factor in the bronchial complcations that follow lung transplantation, the present study indicates that this ischemia is not due to failure of bronchial artery regeneration.