Ion transport in both the frog skin (a high-resistance epithelium) and the rabbit nasal airway epithelium (a low-resistance epithelium) are dominated by electrogenic Na+ absorption via apical membrane amiloride-sensitive Na+ channels, and short-circuit current (ISC) is essentially a measure of Na+ absorption in both epithelia. In both epithelia, mucosal application of the short-chain phospholipid didecanoyl-L-alpha-phosphatidylcholine (DDPC) dose-dependently inhibited the amiloride-sensitive ISC and caused an initial decrease in epithelial conductance (Gt) followed by an increase in Gt to steady-state values above control level. The effects were reversible. It is concluded that DDPC (a) inhibits epithelial amiloride-sensitive Na+ channels and (b) induces an increase in paracellular tight junction conductance. These effects may involve changes in non-specific lipid-protein interactions at the cell membrane level.