1. The effect of temperature on the neuromuscular transmission of the frog's sartorius muscle was studied, with the intracellular electrode, at temperatures between 10°C. and 20°C.2. The end-plate potential diminished, in general, in amplitude as the temperature was lowered. The rate of change in the amplitude was large in the condition that the output of the transmitter from the nerve endings was reduced.3. The probability of appearance of end-plate potential recorded from the preparation soaked in a solution of a low calcium and high magnesium concentration was smaller at lower temperature.4. The effects of temperature on the time course of end-plate potential were considerably great, not only on the rising phase (Q10=2.7), but also on the falling phase of end-plate potential (Q10=2.2). The falling phase of polarized membrane potential was little influenced by temperature.5. The time course of displacement of total charge during the end-plate potential was remarkably lengthened at lower temparature.6. In the eserinized end-plate potential the temperature change had little effect on the falling phase, but the rate of change in the amplitude was greater than that of the non-eserinized end-plate potential.7. The frequency of the spontaneous miniature end-plate potentials had a considerably high temperature coefficient, the mean Q10 being 4.0.8. From these results it may be concluded that an increase in the amplitude of the end-plate potential at higher temperature is mainly due to an increase in output of the transmitter from the nerve endings, and the relatively high temperature coefficient of the falling phase of the end-plate potential is due to a prolongation of transmitter activity at lower temperature.