Pulmonary function in 42 patients with chronic myelogenous leukemia (CML) was tested before and after HLA-matched (39 related, 3 unrelated) allogeneic bone marrow transplantation (BMT) between 1985 and 1999. Pulmonary function tests (PFTs) including ventilatory capacity, lung volumes, and diffusion capacity for carbon monoxide (DLCO) were performed before and 3, 6, 12, and 24 months after BMT, and every 12 months thereafter. Possible pre- and post-BMT risk factors were evaluated for their influence on pulmonary function. Patients were divided into two groups according to their survival duration for more than 12 months or not. Pretransplant PFTs were essentially normal except for mild reduction in DLCO values in the short-term survival group. Overall pulmonary function changes revealed persistent and significant decrease of forced vital capacity (FVC) and DLCO values after BMT. The DLCO values reached abnormal levels (< 80%) and showed a trend of incomplete recovery. Decrease of forced expiratory volume in the first second (FEV1) and vital capacity were also noted but the FEV1/FVC ratio remained within normal limits after BMT. Transient fall of total lung capacity after BMT was noted. However, its values did not reach abnormal levels such as to cause restrictive ventilatory impairment. Possible risk factors including gender, smoking, bronchiolitis obliterans, acute and chronic graft-versus-host disease (GVHD) were found to have significant influences on posttransplant pulmonary function changes by multiple regression analysis. Most patients except those who developed bronchiolitis obliterans were clinically asymptomatic. Development of bronchiolitis obliterans was the most important factor to cause both clinical symptoms and impaired pulmonary function. In summary, pulmonary function changes before and after HLA-matched allogeneic BMT in long-term survivors of CML only showed modest dysfunction. The primary negative presentation with the development of oxygenation defect had no clinical significance in most patients. The influences on the impairment of pulmonary function were multifactorial.