1. Extracellular recording of the electrical activity of mammalian end-plate made it possible to distinguish three different parts on the presynaptic terminal. Bath or ionophoretic application of ionic channel blockers induced specific alterations of electric signals which revealed the localization of classical ionic channels. 2. Sodium channels are restricted to a small area, sharply located after the end of the last myelinated segment and potassium channels are distributed over the rest of the terminal branches. 3. The first direct evidence of the presence of calcium channels at the terminal part of the motor endings was obtained, when potassium channel activity was suppressed. They occupy the same region as potassium channels. 4. Finally, the differential distribution of ionic channels over the terminal and the time-course of calcium current are discussed in relation to transmitter release.