Objective. To testify the phenomenon that large amplitude action potential appears at the early stage of facial paralysis

and to search for the mechanism through clinical and experimental studies. Patients（animals） and methods. The action potentials of the orbicular ocular and oral muscles were recorded in 34 normal persons by electromyogram instruments. The normal range of amplitude percentage was found out according to the normal distribution. One hundred patients with facial paralysis were also studied. The action potentials of facial muscles were recorded in 17 guinea pigs before and after the facial nerve was compressed and the facial nerve was examined under electromicroscope before and after the compression. Results. The amplitude percentage of the suffered side to the healthy side was more than 153 percent in 6 of the 100 patients. Large amplitude action potential occured in 35 per cent guinea pigs which were performed the experiment of facial nerve compression. Electromicroscopic examination revealed separation of the lammae of the facial nerve’s myelin sheath in the guinea pigs which exhibited large amplitude action potential. Conclusion. The facial nerve exhibited a temporary over excitability at the early stage of facial nerve injury in some patients and guinea pigs. If the injury was limited in the myelin sheath

the prognosis was relatively good.