Abstract： Objective To investigate the protein and mRNA expression of HO-1 in the lung tissue of asthmatic rat and the correlation between the percentage of blood carbon monoxide Hb(COHb)and the expressions of HO-1 in the lung tissue of asthmatic rat.Methods Twenty Sprague-Dawley(SD)male rats were randomly divided into 2 groups,control group and asthma group.Each group had 10 rats.The assessment of the percentage content of blood carbon monoxide Hb(COHb)wag performed.The total cell number and differentiation cell numbers in bronchoalveolar lavge fluid(BALF)and the inflammatory cells of airway wall were counted,the protein expressions of HO-1 in airway wall wag detected with immunohistochemistry technique.and the mRNA expressions of HO-1 in airway wall was detected with RTPCR.Results The expression of HO-1 was mainly located in airway epithelium and macrophage.The percentage of the cells in which protein of HO-1was expressed were(5.03±1.22)%,(27.14±4.68)%in two groups.The optical densities of mRNA expression of HO-1 were 0.323±0.05,0.68±0.02.The percent content of blood carbon monoxide Hb(COHb)were(0.45±0.35)%,(3.89±1.15)%.The protein and mRNA expressions of HO-1 and the percent content of COHb in asthmatic group were higher than those of the control group (P＜0.01 respectively).There was a significant positive correlation araong the protein expression of HO-1 in airway wall and the percent content of COHb(r=0.971,P＜0.001),mRNA expressions of HO-1 in lung tissue and the percent content of COI-Ib(r=0.897,P＜0.001).Conclusion The protein and mRNA expressions of HO-1 in the lung tissue,and the percent of COHb in blood were significantly mcreaged in asthmatic rat,which suggested HO-1 may play a significant role in the pathogenesis of asthma.