Electrophysiological studies were performed on the ventral tail nerve of adult rats following intraperitoneal injection of a crude extract of ciguatoxin from known toxic fish flesh. Ciguatoxin induced significant slowing of both mixed and motor nerve conduction velocities and also significant reductions in both motor and mixed nerve amplitudes. Both absolute and supernormal periods were significantly prolonged together with an increase in the magnitude of the supernormal response. These electrophysiological disturbances were modified or blocked by intraperitoneal lidocaine. These findings suggest that lidocaine may have a potential therapeutic application in the treatment of the neurological disturbance in acute ciguatera poisoning in humans.