Patients with high spinal cord injuries may be totally dependent on artificial ventilation. Prolonged use of mechanical devices requires intensive care, which restricts the mobility of these patients. Electrophrenic respiration has been used with success to overcome this difficulty. However, a prerequisite for electrophrenic respiration is a viable phrenic nerve. Patients with spinal cord injuries at the C-3 to C-5 levels do not have a viable phrenic nerve due to gradual degeneration of axons in these nerves. In the present study on cats, the authors caused degeneration in one of the phrenic nerves by sectioning it low in the neck. Then the distal end of the phrenic nerve was anastomosed to the proximal segment of a sectioned brachial nerve. Sixteen to 32 weeks were allowed for the growth of brachial axons into the anastomosed phrenic nerve. Each cat served as its own control because one of the phrenic nerves was left intact. It was observed that pacing of the anastomosed phrenic nerve produced respiration comparable to spontaneous respiration or to respiration induced by pacing the intact phrenic nerve. Lack of rhythmic bursts of electrical activity in the anastomosed phrenic nerve and electromyographic activity in the ipsilateral hemidiaphragm confirmed that the anastomosed phrenic nerve remained disconnected from the respiratory motoneurons. Abundance of collagen matrix in the electron micrographs of the anastomosed phrenic nerve indicated that degeneration of the axons of phrenic motoneurons had occurred and the brachial nerve had grown into the phrenic nerve stump. These results indicate that electrophrenic respiration may be possible in patients with spinal cord injuries at the C-3 to C-5 vertebral levels if the phrenic nerve is kept viable by anastomosing it to a branch of the brachial nerve.