A 33-year-old man suffered chronic ventilatory insufficiency with tetraplegia after an operation for atlantoaxial dislocation. He was alert and his tetraplegia gradually improved. However, continuous mechanical ventilation was necessary for him. Thirteen months after the operation, a diaphragm pacer (Avery Laboratory Inc.) was implanted on the right phrenic nerve in the cervical region. Nineteen days after the implantation of the right side pacer, a left side diaphragm pacer was also implanted. Diaphragm pacing was started two weeks after the second implantation. The pacing period was gradually prolonged and continuous pacing for 9 hours by the right side pacer and three hours by the left side pacer was able to be obtained. One year after implantation, twelve continuous hours of diaphragm pacing became possible. During diaphragm pacing, blood gas analysis was satisfactory and the patient could move sitting on a wheel chair, watch television and write letters using a word processor. We were unable to achieve total ventilatory support for him using these diaphragm pacers. We thought that the main cause of our partial failure originated from the procedure used in implanting the electrode onto the phrenic nerve. Left side pacing needs higher amplitude than that used on the right side to obtain sufficient tidal volume. The patient refused our continuing the left side pacing because of pain around the anterior chest and shoulder. Another problem to be watched is diaphragm fatigue. However, diaphragm pacing has been continued for six years and it has been useful in improving his quality of life.(ABSTRACT TRUNCATED AT 250 WORDS)