Chronic exposure to cigarette smoke (CS) decreases airway surface liquid (ASL) height. Primary human airway epithelial cells from 4 donors (n = 8) were exposed to 30 puffs of whole cigarette smoke (2 cigarettes) every day for 5 days (120 hrs). (A) ASL height was measured one hour after each exposure to CS. ASL height was undisturbed over the course of the reading. *p < 0.05. (B) CFTR present at the plasma membrane was detected by immunoblotting after biotinylation of cell surface proteins (see Methods).