Despite the technique of cardiopulmonary bypass (CPB) improved the development of modern cardiac surgery, many factors during CPB have been reported to induce acute respiratory distress syndrome (ARDS). The present study was to investigate which pro-inflammatory factors involved in the early phase of ARDS. Ten patients underwent valve replacement surgery with or without ARDS were enrolled for analysis of pulmonary function and inflammatory factors release including white blood cell (WBC), neutrophils, CD11b, CD18, interleukin (IL)-8 and tumor necrosis factor-α (TNF-α). The results demonstrated that the ratio of arterial oxygen tension/fraction of inspire oxygen (PaO(2)/FiO(2)) was greatly reduced in ARDS patients, but only the release of TNF-α was significantly increased, which was reversely correlated to the values of PaO(2)/FiO(2). Also, the count of neutrophils adhesive to pulmonary endothelial cells was significantly increased in ARDS patients. Therefore, we concluded that TNF-α was quickly up-regulated and involved in the pathogenesis of CPB-induced ARDS via guiding primed neutrophils to pulmonary interstitium.