Resting membrane potentials (RMP) and resistance to tetrodotoxin (TTX) have been compared in denervated rat soleus muscles and muscles reinnervated with tetrodotoxin-inactive nerves for periods of 15-18 days. RMP's of the two muscle groups exhibited the same low values typical of denervated muscles. Similarly, comparable values of TTX-resistance were found in the two muscle groups, although exceptions with slightly lower values in the innervated-paralyzed muscles were noted. It is concluded that muscle reinnervation restores to normal the membrane properties altered by denervation essentially through the return of muscle activity.