Transmitter release at the Drosophila larval neuromuscular junction may be increased by previous activity of the nerve. This facilitation phenomenon involves at least two processes, one short-term and other long-term. These are shown to based on different mechanisms because (i) a mutant was found that had abnormal long-term facilitation but normal short-term facilitation; and (ii) long-term facilitation was eliminated by tetrodotoxin or by removing external Na+ but short-term facilitation was not. In long-term facilitation, there was a prolonged release of transmitter due to a prolonged Ca2+ sensitivity of the presynaptic terminal after each nerve stimulus. The cause of this is probably accumulation of Na+ inside the nerve terminal.