Objective To investigate the protective effect of genistein on endotoxin-induced acute lung injury in rats,and explore the underlying mechanisms.Methods Thirty-two male Sprague-Dawley rats were randomly divided into four experimental groups: saline control(S), genistein alone(G),lipopolysaccaride(LPS) alone(L),and genistein pretreatment(G+L).Each treatment group consisted of eight animals.Animals were observed for 6h after LPS challenge,and the wet/dry(W/D) weight ratio of the lung and the protein contents of the bronchoalveolar lavage fluid(BALF) were used as indexes of lung injury.Neutrophil recruitment and activation were evaluated by BALF cellularity and myeloperoxidase(MPO) activity.RT-PCR analysis was performed with lung tissue to assess the gene expression of ICAM-1.The histopathologic changes were also observed using the H&E stains of lung tissue.Results Lung injury parameters,including the wet/dry weight ratio and protein content in BALF,were significantly higher in the L group than in the S group(P