We report the case of a 40-year-old female patient after allogeneic bone marrow transplantation due to chronic myeloid leukaemia. One year after transplantation, the symptoms of recurrent bronchial and lung infections, inefficiently treated with antibiotics, appeared. The disease was further complicated due to hepatic insufficiency resulting from mixed infection with HBV and HCV as well as because of chronic graft-versus-host disease (GvHD). Chest computed tomography and pulmonary function tests seemed to confirm BOOP diagnosis, but despite three-time-conducted bronchoscopy, histopathological diagnosis was not obtained. When admitted to the Pulmonary Department, the patient was in serious condition caused by intensifying respiratory failure. After multidrug therapy enabling to control opportunistic infections, high doses of corticosteroids were administered intravenously resulting in partial health improvement. The patient seems to be afflicted with BOOP of mixed aetiology. Treatment efficiency may confirm the necessity of rapid BOOP diagnosis even if histopathological diagnosis is not obtainable.