Objectives/Hypothesis: Although the pathophysiology leading to rhinosinusitis is complex, evidence indicates that decreased mucociliary clearance (MCC) is a major contributing feature. Normal respiratory epithelial MCC is an important host defense mechanism that is dependent on proper ciliary beating and the biological properties of the airway surface liquid (ASL). The role that tobacco smoke exposure plays as an inhibitor of MCC has yet to be elucidated. The present study investigates the consequences of cigarette smoke exposure on ciliary function and transepithelial chloride (Cl-) secretion, a major determinant of ASL. Study Design: In vitro investigation. Methods: Well-characterized primary murine nasal septal epithelial (MNSE) and human sinonasal epithelial (HSNE) cultures were exposed to cigarette smoke condensate (CSC) and compared to control cultures. Effects on ciliary beat frequency (CBF) and Cl- secretion were investigated using pharmacologic manipulation. Results: Change in forskolin-stimulated current (ΔISC), representing transepithelial Cl- secretion, was significantly decreased in CSC exposed MNSE (14.97 ± 1.2 μA/cm2 vs. control, 19.1 ± 1.56 μA/cm2 [P = .04]) and HSNE (2.68 ± 0.79 μA/cm2 vs. control, 10.8 ± 1.73 μA/cm2) cultures (P = .001). Forskolin-stimulated CBF was also significantly reduced when acutely exposed to CSC (5.64 ± 0.06 Hz vs. control 7.15 ± 0.18 Hz). Conclusions: The present study provides direct evidence that tobacco smoke diminishes two major components of MCC. This links tobacco smoke as a potential contributing and/or exacerbating factor in exposed individuals with chronic rhinosinusitis. © 2009 The American Laryngological, Rhinological and Otological Society, Inc.