Objective To investigate the effect of ketamine on lipopolysaccharide ( LPS)-induced activation of nuclear factor-kappa B (NF-kB) in rat lung in vivo.Methods Twenty-four adult Wistar rats weighing 260-310 g were randomly divided into four groups with 6 animals in each group : (Ⅰ) control group received normal saline (NS) 0.3 ml iv;(Ⅱ) LPS group received LPS 8 mg?g-1 in 0.3 ml of NS iv + LPS 100?g?kg-1 in 0.2 ml of NS introduced into trachea;(Ⅲ) ketamine group A received ketamine 4 mg?kg-1 in 0.3 ml of NS iv 30 min after LPS + ketamine 4 mg?kg-1 ip after an interval of 60 min; (Ⅳ) ketamine group B received ketamine 8 mg?kg-1 iv and ip instead of 4 mg?kg-1 in groupⅢ. The animals were sacrificed 240 min after NS or LPS injection and chest was immediately opened. 10 ml of blood was removed from left heart for determination of MDA and NO2 / NO-3 concentration. The NF-kB activation of nuclear protein extracted from the lung was measured by EMSA. 99Tc was used to determine the pulmonary vascular permeability.Results NF-KB activation in the lung, serum MDA and N0-2 / NO-3 and the pulmonary vascular permeability were significantly increased in LPS group as compared with those in control group (P