BACKGROUND: In recent years, surgeons have advocated root or trunk repair of avulsed nerve roots for overall recovery. However, donor nerves pose a major problem, because they do not contain adequate numbers of axons. Moreover, the procedures lead to nerve deficits in the donor nerve following transplantation. OBJECTIVE: To observe whether axonal regeneration occurs by end-to-side neurorrhaphy in the peripheral nerve and spinal cord. DESIGN, TIME AND SETTING: A neuroanatomical, randomized, controlled, animal study was performed at Functional Anatomy Lab in Nagoya University School of Medicine from May 2002 to July 2003. MATERIALS: Fluorogold was purchased from Fluorochrome, LLC, USA. BX50 light microscope and fluorescent microscope were purchased from Olympus, Japan. METHODS: A total of 21 rats were randomly divided into three groups, and the posterior avulsion injury model (C(6-8)) of the brachial plexus was performed. In the ventral root graft group, the avulsed C(7) ventral roots were reanastomosed to the small anterior lateral aspect window of the spinal cord via nerve grafts. In the dorsal root graft group, the C(7) dorsal roots were reanastomosed at the small pia mater window of the posterior lateral aspect of the spinal cord via nerve grafts. In the control group, the avulsed nerve roots were not repaired. MAIN OUTCOME MEASURES: The nerve grafts were collected from the ventral and dorsal root graft groups, and the C(7) proximal nerve end was collected from the control group. Acetylcholinesterase staining was performed on the tissue. Fluorogold retrograde tracing technique was applied to determine the origin of the regenerating axons. RESULTS: Results showed that acetylcholine-positive axons existed in nerve grafts of the ventral and dorsal root graft groups. However, axons were not found in the avulsed nerve roots of the control group. Fluorogold retrograde tracing confirmed the presence of fluorogold-containing neurons in the ventral and dorsal horn of the ventral and dorsal root graft groups. Fluorogold-positive neurons were not observed in the control group. CONCLUSION: End-to-side neurorrhaphy induced axonal regeneration from the spinal cord to the peripheral nervous system.