Three types of injuries were inflicted upon the right recurrent laryngeal nerves of ten dogs. The larynges of these dogs were observed regularly for six months or more by direct laryngoscopy, EMG recordings from the thyroarytenoid muscle, and conduction studies of recurrent laryngeal nerves. Control dogs, whose right recurrent larngeal nerves had been resected segmentally, never regained any normal functions visually or electromyographically. All the dogs with the crushed injury showed complete return of normal functions except one dog, which returned partially. The dogs having a section and neuorrhaphy showed abnormal medial bulging and shivering motion of the right vocal cord during inspiration. From the EMG examination, inspiratory discharges were seen at the right thyroarytenoid muscle simultaneously with the abnormal motion of the right vocal cord. After 6 months, the specimens of the right recurrent laryngeal nerve were obtained and morphological studies were done by light microscopy and electron microscopy. The penetration rate of the myelinated fibers through the neuorrhaphy site was about 60 per cent.