The effects of denervation on the electrical membrane properties of fish red muscle were investigated. Forty to fifty hours after denervation, miniature endplate potentials disappeared abruptly and field stimulation of the nerve within the muscle failed to evoke endplate potentials, indicating that transmission failure occurred at this time. The membrane resistance of the red muscle fibre increased after denervation. Normally innervated fish red muscles do not generate action potentials in response to either nerve or direct muscle stimulation. However, approximately 3 weeks after nerve sectioning, action potentials could be induced in the muscles. The action potential was sodium-dependent, and was sensitive to tetrodotoxin. Actinomycin D injected in the early phase after operation suppressed the induction of the action potential. These results indicate that RNA synthesis is preliminary to the induction of the action potential mechanism, and that this mechanism is under neural control.