['Chronic obstructive pulmonary disease is a risk factor for postoperative lung injury. Contradictory results have been published about leukocyte filtration (LF) because of the heterogeneity of patients and interventions, type of LF, and comorbidities.', 'Sixty patients with mild moderate chronic obstructive pulmonary disease (forced expiratory volume in 1 second 40% to 80%) undergoing aortic valve surgery were randomly assigned to receive systemic arterial and cardioplegic LF during cardiopulmonary bypass (group L, 30 patients) or standard cardiopulmonary bypass (group S). Perioperative interleukin-6, interleukin-8, and tumor necrosis factor-alpha were sampled at different time points. The PaO2/inspired oxygen fraction (FiO2) and alveoloarterial oxygen gradient (AaDO2) were measured preoperatively, at intensive care unit arrival, and at 24, 48, and 72 hours postoperatively; lung compliance was measured after intubation, at intensive care unit arrival, and at 4 and 8 hours postoperatively; and radiographic lung injury score was determined preoperatively and at 24, 48 and 72 hours. Length of intubation, intensive care unit stay, hospital stay, need for noninvasive positive-pressure ventilation, acute lung injury, and pneumonia were recorded. Repeated-measures analysis of variance assessed group, time, and group by-time interactions.', 'Preoperative and intraoperative data were comparable. Proinflammatory cytokine leakage was reduced by LF. Group L showed shorter intubation time (median 9.5 hours versus group S, 15.0 hours; p=0.0001), and intensive care unit length of stay (median 19.0 hours versus group S, 24.5; p=0.0001), lower need for noninvasive positive-pressure ventilation (5 of 30, 16.7%, versus 12 of 30, 40%; p=0.042). The AaDO2, PaO2/FiO2, lung compliance, and radiographic lung injury score worsened early postoperatively, followed by progressive improvements (time p≤0.001 for all). Such decline of AaDO2, PaO2/FiO2, lung compliance, and radiographic lung injury score was significantly attenuated by LF (group by-time p=0.0001 for AaDO2, PaO2/FiO2, and lung compliance; p=0.004 for radiographic lung injury score).'] Does leukocyte filtration ameliorate the inflammatory response in patients with mild to moderate lung dysfunction?