Background. One third of human lung allografts develop chronic rejection manifested as obliterative bronchiolitis. Heterotopically transplanted allogeneic murine tracheas develop obliterative airway disease (OAD) leading to a lesion resembling human obliteratire bronchiolitis. The purpose of this study was to determine the T-cell and major histocompatibility complex (MHC) molecule requirements of murine OAD. Methods. BALB/c allografts and C57BL/6 (B6) isografts were transplanted into B6 severe combined immunodeficient (SCID) and B6 wild-type (WT) recipients. MHC class I-discrepant bml grafts, class II-discrepant bm12 grafts, and F1(bm1xbm12) (F1) grafts also were transplanted into B6 WT recipients. Grafts were harvested between days 5 and 56 following transplantation and evaluated histologically. Results. Complete MHC-disparate allografts placed in WT recipients had significantly more disease than similar allografts in SCID recipients, and the latter were indistinguishable from isografts in either WT or SCID recipients, indicating a lymphocyte dependence on the disease development. Pathology was significantly more severe in bin1 and F1 allografts than in isografts recovered from B6 recipients, but bm12 allografts appeared no different than isografts. T-cell inflitrates in these bm12 allografts contained only CD4+ cells, whereas infiltrates in the BALB/c, bm1, and F1 allografts manifesting OAD contained both CD4+ and CD8+ cells. No grafts had significant B-cell infiltration. Conclusions. These findings suggest that OAD relies on a host T-cell response that includes CD8+ cells, directed against allo-class I- bearing donor cells within the graft.