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Some aromatic amine local anesthetics are a kind of amphiphilic ion. Binding of local anesthetics, dibucaine (DC), bupivacaine (BC), and lidocaine (LC) to a dipalmitoylphosphatidylcholine (DPPC) bilayer membrane was studied by potentiometry with ion-selective electrodes sensitive to DC, BC and LC cations, respectively. The DPPC membrane-buffer partition coefficient was directly determined as a function of the anesthetic concentration and the temperature. The DPPC bilayer underwent a thermotropic pretransition from the lamellar gel phase to the ripple gel phase as well as a main transition from the ripple gel phase to the liquid crystal phase. The partition coefficients of anesthetics at pH 5.5 varied with the temperature, namely the bilayer phases. Potentiometry using an ion-selective electrode sensitive to amphiphilic ions is effective for the detection of a bilayer phase transition through partition coefficients.