The effects of antidiuretic hormone (ADH) on the rate of transepithelial active Na transport J Na a and the rate of suprabasal O 2 consumption J r sb were studied in paired hemiskins of frog. Within some 30 min following administration of ADH both J Na a and J r sb increased to near-maximal levels and then remained stable for at least an hour. On symmetric perturbation of the transepithelial electrical potential Δψ at 6-min intervals, the dependence of J Na a and J r sb on Δψ was near-linear, both in control and experimental hemi-skins. The stability and near-linearity of the system permitted systematic analysis of the parameters of linear non-equilibrium thermodynamic (NET) and electrical equivalent circuit (EC) formulations. ADH (100 mU/ml)-stimulated two of the three NET phenomenological L coefficients, as well as A, the affinity (negative Gibbs free energy) of a metabolic reaction driving transport. Observations at partially depressed levels of transport indicated that the effects on kinetic and energetic factors are to some extent discrete. EC analysis showed stimulation of the amiloride-sensitive conductance K a , but not of the apparent electromitive force of Na transport ‘ E Na ’. Similar effects were produced by 10 mU/ml of ADH or by 10 mM dibutyryl cyclic AMP, although less marked effects on the L coefficients were noted with the lower concentration of hormone. It is suggested that, in contrast to EC analysis, the NET formulation distinguishes between kinetic and energetic determinants of transport, supporting a dual mechanism of action of ADH.