The chloride current across the isolated epithelium from saline-acclimated Bufo viridis toads was studied using the extracellular vibrating probe technique. Local peak current densities varying between 5 and 100 microA/cm2 were recorded over subpopulation of mitochondria-rich cells, but never over granulosum cells. These local transepithelial currents had characteristics similar to the activated chloride current observed in the whole skin (Katz, U. and Larsen, E.H. (1984) J. Exp. Biol. 109, 353-371). Replacement of the apical Ringer with chloride-free (nitrate) ringer resulted in reversible reduction in the current at the mitochondria-rich cells. It is concluded that the mitochondria-rich cells are the principal site of passive chloride conductance across the epithelium.