Avulsion of nerve roots from the spinal cord is widely regarded as an untreatable injury. However, a series of experiments in animals has shown that, if continuity is restored between spinal cord and ventral roots, axons from spinal motor neurons can regrow into the peripheral nerves with recovery of motor function. These observations were applied in the treatment of a man with avulsion of the 6th cervical (C6) to 1st thoracic roots due to brachial plexus injury. Two ventral roots were implanted into the spinal cord through slits in the pia mater, C6 directly and C7 via sural nerve grafts. Voluntary activity in proximal arm muscles was detected electromyographically after nine months and clinically after one year. After three years the patient had voluntary activity (with some co-contraction) in the deltoid, biceps, and triceps muscles. To determine whether the improvement was due to spontaneous recovery from C5, the C5 root was blocked pharmacologically, and the results indicated that the repaired roots were contributing substantially to motor function. Repair of spinal nerve roots deserves further exploration in management of brachial plexus injury.