A 17-year-old man diagnosed as acute myelogenous leukemia (M5a) underwent allogeneic bone marrow transplantation from his HLA-identical, MLC non-reactive sister on the occasion of the second complete remission. On day 14 engraftment was confirmed by karyotypic expression. The patient had no evidence of acute graft-versus-host disease (GVHD), therefore cyclosporine A was discontinued on day 62. Having complained of cough and dyspnea by day 100, the patient was diagnosed as interstitial pneumonitis (IP) based on chest X-ray findings. However, no other typical signs of chronic GVHD were present except for modest abnormality of liver function. Since there was no evidence of infection on bronchofiberoscopic examination and prednisolone was very effective, it was considered that the IP might be pulmonary disease of chronic GVHD. It has been reported that HLA-DR which is not normally found, is expressed on epithelial tissues of the patient with GVHD. In this case alveolar epithelial cells were positive for LN-3 (anti-HLA-DR). In conclusion, pulmonary disease in this case may represent a possible manifestation of chronic GVHD, thus suggesting that the current case could provide information to ascertain the mechanism of chronic GVHD.