AIM: To investigate the role of infiltration of macrophages and expression of intracellular adhesion molecule-1 in the pathogenesis of oleic-acid-induced acute lung injury rats. METHODS: The rats were subjected to injection of oleic acid (oleic acid group) or saline solution (control). After injecting oleic acid or saline for 4 hours, the PaO 2 of the left heart, lung permeability index(LPI), the number of macrophage and the levels of soluble intercellular molecule-1 (sICAM-1) in the bronchial alveolar lavage fluid (BALF) were measured. The levels of expression of ICAM-1 mRNA were evaluated by in situ hybridization and the degree of macrophage infiltration and the expression of ICAM-1 were evaluated by double staining immunocytochemistry. RESULTS: The PaO 2 of the oleic acid group was significantly lower than that of the control group (P