Objective:To investigate the concentration of pulmonary surfactant-associated protein D ( SP-D) and interleukin-8 (IL-8) in the bronchoalveolar lavage fluid (BALF) of ACOS patients undergoing mechanical ventilation (MV). Methods:38 patients with ACOS undergoing MV were involved in the study. According to the APACHEⅡscore, the patients were divided into the remission group (n=20) and the aggravation group (n=18). BALF was collected on the 1st and 5th days after MV. The content of IL-8 and SP-D in BALF was measured by ELISA. The levels of IL-8 and SP-D in BALF of the patients with different severity were compared. Results:The level of SP-D was significantly higher on the 5th day than on the 1st day in the remission group,and it decreased more ob-viously in the worsening group (P<0. 05). The level of IL-8 decreased gradually in the remission group but increased gradually in the worsening group. The level of SP-D was negatively correlated with IL-8 level and APACHEⅡ score. Conclusion:The findings suggest that the levels of SP-D and IL-8 in BALF are correlated with prognosis of ACOS patients undergoing MV,and it may prove to be useful as a guidance of therapy and prognosis.