Salt and water absorption and secretion across the airway epithelium are important for maintaining the thin film of liquid lining the surface of the airway epithelium. Movement of Cl across the apical membrane involves the CFTR Cl channel; however, conductive pathways for Cl movement across the basolateral membrane have been little studied. Here we determined the regulation and single channel properties of the basolateral Cl conductance (G_Cl) in airway surface epithelia using epithelial cultures from human or bovine trachea and freshly isolated ciliated cells from the human nasal epithelium. In Ussing chamber studies, a swelling-activated basolateral G_Cl was found, which was further stimulated by forskolin, and blocked by DPC = sucrose > flufenamic acid = niflumic acid = glibenclamide > CdCl₂ = NPPB = DIDS = ZnCl₂ > tamoxifen > DNDS. In whole cell patch clamp experiments, three types of G_Cl were identified 1) a voltage-activated, DIDS- (but not Cd) blockable and osmosensitive G_Cl, 2) an inwardly rectifying, hyperpolarization-activated and Cd-sensitive G_Cl, and 3) a forskolin-activated, linear G_Cl, which was insensitive to Cd and DIDS. In cell-attched patch clamp recordings, the basolateral pole of isolated ciliated cells expressed three types of Cl channels: 1) an outwardly rectifying, swelling-activated Cl channel, 2) a strongly inwardly rectifying Cl channel, and 3) a forskolin-activated, low-conductance channel. We propose that depending on the driving force for Cl across the apical membrane, basolateral Cl channels confine Cl^- secretion or support transcellular Cl^- absorption.