Active Na⁺ absorption across rumen epithelium comprises Na⁺/H⁺ exchange and a non selective cation conductance (NSCC). Luminal chloride is able to stimulate Na⁺ absorption which has been attributed to an interaction between Cl^-/HCO₃^- and Na⁺/H⁺ exchangers. However, isolated rumen epithelial cells also express a Cl^- conductance. We investigated whether Cl^- has an additional effect on electrogenic Na⁺ absorption via NSCC. NSCC was estimated from Isc across epithelia of goat and sheep rumen in Ussing chambers. Epithelial surface pH was measured with 5-N-hexadecanoyl-aminoflorescein. Membrane potentials were measured with microelelectrodes. Luminal but not serosal Cl^- stimulated the Ca²⁺ and Mg²⁺ sensitive Isc. This effect was independent of the replacing anion (gluconate or acetate) and of the presence of bicarbonate. The mean surface pH of rumen epithelium amounted to 7.47±0.03 in a low Cl^- solution. It was increased by 0.21 pH units when luminal Cl^- was increased from 10 to 68 mmol/l. Increasing mucosal pH from 7.5 to 8.0 also increased the Ca²⁺ and Mg²⁺ sensitive Isc and Gt and reduced the fractional resistance of the apical membrane. Luminal Cl^- depolarized the apical membrane of rumen epithelium. 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) reduced the divalent cation sensitive Isc, but only in low Cl^- solutions. The results show that luminal Cl^- can increase the microclimate pH via apical Cl^-/HCO₃ ^- or Cl^-/OH^- exchangers. Electrogenic Na⁺ absorption via NSCC increases with pH explaining part of the Cl^- effects on Na⁺ absorption. The data further show that the Cl^- conductance of rumen epithelium must be located at the basolateral membrane.