The electrical response of the snail retractor muscle elicited by stimulating either the muscle or the nerve was recorded. In both cases the response is found to be composed of two component potentials, the fast potential, which is often recorded as a diphasic form, and the slow monophasic potential. The former is attributed to the muscle action potential and the latter to the neuromuscular junctional potential, because the former shows refractoriness after the preceding response, and the latter summates when two stimuli are delivered to the nerve or the muscle with an appropriate interval. The response to indirect stimulation shows depression in the magnitude of the response after the preceding stimulus, and this depression persists for as long as a few minutes. When the test stimulus of just suprathreshold strength is applied to the nerve, this fails completely to elicit any response about 100 msec. after the conditioning response.