SLC26 proteins function as anion exchangers and Cl⁻ channels. SLC26A9 has been proposed to be a constitutively active and CFTR‐regulated anion conductance in human bronchial epithelia. This positive interaction between two Cl⁻ channels has been questioned by others and evidence has been provided that CFTR rather inhibits the transport activity of SLC26A9. We therefore examined the functional interaction between CFTR and SLC26A9 in polarized airway epithelial cells and in non‐polarized HEK293 cells expressing CFTR and SLC26A9. We found that SLC26A9 provides a constitutively active basal Cl⁻ conductance in polarized grown CFTR‐expressing CFBE airway epithelial cells, but not in cells expressing F508del‐CFTR. In polarized CFTR‐expressing cells, SLC26A9 also contributes to both Ca²⁺‐ and CFTR‐activated Cl⁻ secretion. In contrast in non‐polarized HEK293 cells co‐expressing CFTR/SLC26A9, the baseline Cl⁻ conductance provided by SLC26A9 was inhibited during activation of CFTR. SLC26A9 and CFTR behave differentially in polarized and non‐polarized cells, which may explain earlier conflicting data. J. Cell. Physiol. 227: 2323–2329, 2012. © 2011 Wiley Periodicals, Inc.