Abstract 1. 1. In an isolated nerve-skin preparation of Rama temporaria L. electrical stimulation of the nerves gives a cyclic variation of the skin potential. 2. 2. The type of response obtained is in direct relation with the level of polarization of the skin. Above 30 mV one observes a depolarization phase followed by a hyper-polarization phase, while below 30 mV the hyper-polarization phase is present only. 3. 3. When SO 4 ions replace in equivalent amount the Cl ions in the physiological saline used, the hyper-polarization phase is abolished. 4. 4. Among the various pharmacologically active compounds used, noradrenaline is the only substance imitating more or less closely the effect of an electrical stimulation. 5. 5. The results are discussed in the light of the scheme presented by Ussing, 1960.