OBJECTIVE: To study the role of cell adhesion molecule CD44 in the lung on airway inflammatory response in rats with asthma. METHODS: Thirty-two Sprague-Dawley rats were randomly divided into normal control and asthma groups. Asthma was induced by repeated inhalation of ovalbulium. CD44 expression in the lung was detected by semi-quantitatively reverse transcription-polymerase chain reaction (RT-PCR) and immuno-histochemical staining 1 week and 2 weeks after ovalbulium challenge. Differential leukocytes (mononuclear phagocytes, neutrophils, eosinophils, and lymphocytes) in bronchoalveolar lavage fluid (BALF) were counted. RESULTS: CD44 expression in the lung increased 1 week after ovalbulium challenge (P<0.05) and increased more significantly 2 weeks after ovalbulium challenge (P<0.01) compared with that in the control group. The percentages of lymphocytes and eosinophils in BALF increased, while the percentage of BALF mononuclear phagocytes decreased significantly 1 week and 2 weeks after ovalbulium challenge in the asthma group compared with those in the control group (P<0.05). An increased percentage of neutrophils was found 1 week after ovalbulium challenge in the asthma group compared with the control group (P<0.05). CD44 expression in the lung was positively correlated with the percentages of lymphocytes and eosinophils in BALF in the asthma group 1 week and 2 weeks after ovalbulium challenge, in contrast, lung CD44 expression was negatively correlated with the percentage of mononuclear phagocytes in the asthma group 1 week after ovalbulium challenge. CONCLUSIONS: CD44 was over-expressed in the lung and closely related to inflammatory infiltration in rats with asthma. CD44 may play an important role in the development of airway inflammatory in asthma.［Chin J Contemp Pediatr, 2009, 11 (2):142-145］