METHODS: After approval by the institutional ethical committee, a prospective randomized study was performed to compare nine patients undergoing coronary artery bypass grafting (CABG) using leukocyte filtration in the arterial line (LG-6, Pall Biomedical Products) and eleven others submitted to standard CPB. Chest CT, oxygenation analysis and a complete leucocyte count were performed before surgery. After intravenous anesthesia induction, patients were mechanically ventilated with tidal volume of 8 mL.kg-1, with FiO2 0.6, and PEEP of 5 cm H2O, except during CPB. Haemodynamic data, PaO2/FiO2, shunt fraction, interleukins, elastase and myeloperoxidase were evaluated before and after CPB, at the end of surgery, 6, 12 and 24 hours after surgery. Chest CT was repeated on the first postoperative day. Data were analyzed using two-factor ANOVA for repeated measures.