Objective To examine the effects of propofol, midazolam and pyrrolidine dithiocarbamate (PDTC) on acute lung injury (ALI) induced by normothermic cardiopulmonary bypass (CPB) .Methods Twenty-six adult SD rats of both sexes weighing 350-450 g were randomly divided into 4 groups: group I midazolam (MZ, n = 7); group 11 MZ + PDTC ( n = 7); group III propofol (PROP, n = 7) and group IV sham operation ( n = 5). The animals were premedicated with intraperitoneal (i.p.) atropine 1 mg?kg-1 and anesthetized with i.p. midazolam 4 mg?kg-1 and fentanyl 150?g?kg-1 in group I , II and IV or with i.p. propofol 30mg?kg-1 and fentanyl 150 ?g?kg-1 in group III . CPB was performed at a flow rate of 100 ml?kg-1? min-1 for 60 min. In group II PDTC 100 mg?kg-1 was given i.p. 30 min before CPB. In sham operation group the animals were anesthetized, intubated and mechanically ventilated but underwent no CPB. Arterial blood samples were taken before initiation of CPB (T1 ) , at the end of CPB (T2) and 60 min after CPB (T3) for blood gas analysis and determination of the expression of CD11b on neutrophils by flow cytometry. Respiratory index (RI) was calculated at T1 and T3 . The animals were killed at 60 min after CPB and the lungs were removed for broncho-alveolar lavage. PMN count, protein and IL-8 concentration of broncho-alveolar lavage fluid (BALF) and lung MDA content were determined. The lung histology was also examined. Results RI was significantly increased at T3 as compared to T1 in group MZ ( P