A large defect in the thoracic trachea was produced by rejecting 10 rings of tracheal cartilage in each of 11 adult mongrel dogs. An allograft of the five tracheal rings was interposed in this site via end-to-end anastomosis and then wrapped with the pedicled omental flap. These animals received no immunosuppressive therapy. The pseudostratified tracheal epithelia were remained and the graft revascularization through the omental pedicle proved to be established within about one week after

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... y without immunosuppression. Marked mononuclear cell infiltration was observed beneath the epithelia and around the capillaries in the subepithelial layer over one week after surgery, which was followed by phagocytosis of the tracheal cartilages by macrophages. After the completion of rejection reaction, inflammation finally induced scarring or necrosis of the tracheal allograft, resulting in asphyxia or perforation. Only one animal survived 71 days after surgery without graft trouble. However, even in this animal, weak rejection reaction was observed microscopically and the structure of the graft was not that of the normal trachea. We think these results suggest that allotransplantation of trachea induces rejection, and therefore, that the use of immunosuppressants is necessary.