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Cigarette smoking is the dominant risk factor for chronic obstructive pulmonary disease (COPD). However, only 10-15% of smokers develop the disease and early changes within the airways are poorly defined. We aimed to compare cell profiles in induced sputum (IS) from asymptomatic smokers to that from healthy subjects, and to ascertain whether or not inflammatory cells in IS are related to lung function and smoking habit. We recruited 34 heavy, non-allergic asymptomatic smokers with normal lung function and 15 healthy volunteers, who performed lung function tests and IS by hypertonic saline (3%) solution. In smokers, significantcorrelation between pack-years and FEF25-75 (rs = -0.43, P < 0.02) was found. In IS, smokers had higher counts of macrophages (P < 0.01) and eosinophils (P < 0.02), when compared to those of healthy subjects. Additionally, eosinophils were found in IS of 14 out of 34 smokers, with eosinophils had a higher pack-years (31 +/- 25 vs. 13 +/- 10, P = 0.02) and lower FEF 25-75% value (78% +/- 34 vs. 100% +/- 23. P < 0.04). when compared to smokers without eosinophils. Additionally, on the basis of regression equations by stepwise multiple regression analysis, eosinophils were predicted by pack-years (r2 = 0.41). Our results showed that asymptomatic smokers have evidence of inflammatory cells in IS samples. In addition, we found thatthe degree of eosinophilic inflammation is related to early changes of lung function and can be predicted by smoking habit.