The role of the cystic fibrosis transmembrane conductance regulator (CFTR) in cAMP-stimulated secretion across the murine duodenum was investigated. Serosal-to-mucosal flux of (J _s→m, in μeq ⋅ cm⁻² ⋅ h⁻¹) and short-circuit current (I _sc; in μeq ⋅ cm⁻² ⋅ h⁻¹) were measured by the pH stat method in duodenum from CFTR knockout [CFTR(−)] and normal [CFTR(+)] mice. Under control conditions, forskolin increased J _s→m andI _sc (+1.7 and +3.5, respectively) across the CFTR(+) but not CFTR(−) duodenum. Both the forskolin-stimulated ΔJ _s→m and ΔI _sc were abolished by the CFTR channel blocker 5-nitro-2-(3-phenylpropylamino)benzoate, whereas inhibition of luminal Cl⁻/ exchange by luminal Cl⁻ removal or DIDS reduced theJ _s→m by ∼18% without a consistent effect on the ΔI _sc. Methazolamide also reduced theJ _s→m by 39% but did not affect the ΔI _sc. When carbonic anhydrase-dependent secretion was isolated by using a CO₂-gassed, -free Ringer bath, forskolin stimulated the J _s→m andI _sc (+0.7 and +2.0, respectively) across CFTR(+) but not CFTR(−) duodenum. Under these conditions, luminal Cl⁻ substitution or DIDS abolished theJ _s→m but not the ΔI _sc. It was concluded that cAMP-stimulated secretion across the duodenum involves 1) electrogenic secretion via a CFTR conductance and2) electroneutral secretion via a CFTR-dependent Cl⁻/ exchange process that is closely associated with the carbonic anhydrase activity of the epithelium.