Electroneuronography, an objective electrophysiologic measurement of a muscle compound action potential, is used to assess the integrity of facial nerve and to determine prognosis for recovery in patients with facial paralysis. This study was performed to evaluate the pattern of electrophysiological change of the injured facial nerve and interrelationship between electroneuronographic data and histopathological findings. Facial nerves of 19 rabbits were injured by clamping with a mosquito or by multiple stabbing with a Bard Parker #11 blade. Electroneuronography was performed at postoperative 1,2,3,4 and 5 days and the nerves were prepared for pathological evaluation. The results were as follows : 1) There was rapid decrease of electroneuronographic data at postoperative 1 day and maximum decrease at postoperative 2 day. Thereafter, the data maintained unchanged until postoperative 5 day. 2) Pathological findings of degenerated fibers were myelin infolding, disruption of myelin lamellae, myelin cleft, and total breakdown of myelin ring. These changes began later than change of electroneuronography and progressed gradually thereafter. 3) There was significant interrelationship between electroneuronographic data and degree of nerve degeneration at postoperative 4 day : The electroneuronographic data was lower when the degenerative change of the facial nerve was severe.