The presence or absence of the denervation is one of the important factors to determine the prognosis of peripheral facial nerve palsy and it is generally accepted that the denervation becomes apparent within 2 weeks from the onset of illness. In the present study, 62 cases with denervation in which nerve excitability test (NET) was possible within 1 week from the onset of illness were selected for analysis. Although 47 cases exhibited the denervation within 2 weeks, it was first detected after 2 weeks in other 15. Although the prognosis was far better in the latter group, 2 cases exhibited the unfavorable recovery. These results indicate the importance of NET even 2 weeks after the onset of illness.