BACKGROUND: To evaluate whether ambroxol administered orally during the perioperative period has a protective effect against postoperative pulmonary dysfunction in on-pump coronary artery bypass surgery. METHODS: Fifty younger patients without known pulmonary disease were randomly assigned into 2 groups. In ambroxol group (n = 25), patients were given ambroxol for a week before and after the elective coronary artery bypass grafting. In control group (n = 25), placebo was given. Groups were compared with respect to pulmonary function tests (PFTs), lecithin/sphingomyelin (L/S) ratio in the bronchoalveolar lavage fluid, arterial blood gases, and incidence of perioperative morbidity. PFTs were performed before medication and repeated on the postoperative seventh day. Bronchoalveolar lavage fluid was obtained just before cardiopulmonary bypass and within the first postoperative hour. Room air arterial blood gases were checked before and 2 days after the operation. RESULTS: Postoperative lecithin/sphingomyelins were significantly lower than the preoperative values in both groups, but differences between the groups in either preoperative or postoperative measurements were not significant. Although preoperative PaO2 in both groups was similar, it was significantly lower in control group on postoperative second day (62.4 +/- 7.1 vs. 55.2 +/- 6.4 mm Hg, P < 0.05). In either groups, postoperative forced vital capacity and forced expiratory volume in 1 second were significantly lower than preoperative values with a more prominent decrease in control group. Perioperative morbidity was similar. CONCLUSIONS: In on-pump coronary artery bypass grafting, ambroxol improves postoperative PFTs and PaO2 levels without any significant clinical implication, and it exerts these effects possibly in ways other than surfactant modulation.