Chronic obstructive pulmonary disease (COPD) involves disease of small airways with an increase in airway smooth muscle sensitivity to spasmogens and with structural changes described as airway remodeling. We have investigated the effect tobacco smoke (TS) exposure on the structure and function of small airways in rats, and have also studied the role of interleukin (IL)-13 in this response. Precision-cut lung slices (230-280 µm) were prepared from male Sprague-Dawley rats after acute (3 days) or chronic (8 or 16 weeks) daily exposure to TS, or air. Carbachol (CCh) and 5-hydroxytryptamine (5HT) concentration-responses were performed on airways (50-400 µm diameter). The effect of IL-13 in vitro on small airway sensitivity to CCh and 5HT was also determined. Acute exposure to TS did not affect the sensitivity of the intrapulmonary airways to either spasmogen. After 8 weeks of TS exposure, airway hyper-responsiveness (AHR) to CCh was evident (log EC50 CCh: air=0.22µM, TS=-0.12µM, P=0.019); AHR to 5HT was also observed after 16 weeks exposure to TS (air=-0.85µM, TS=-1.06µM, P=0.038). Chronic TS exposure increased airway wall SMA content which correlated with increased expression of IL-13 and transforming growth factor (TGF)-1 in the lung tissues. In vitro incubation with IL-13, but not TGF-1, induced changes in small airway sensitivity to both CCh and 5HT. Chronic TS exposure induces increased responsiveness in intrapulmonary airways of rats that in part may be mediated by an increase in IL-13.