Post-tetanic potentiation (PTP) lasting several minutes is produced by high frequency intracellular activation of mechanosensory neurons. Control procedures suggest that the PTP involves a homosynaptic mechanism, restricted to the active synapses. The capacity for PTP appears to be a general property of mechanosensory neurons in this animal since it is found in separate sensory populations innervating the tail, head, and siphon of Aplysia.