Introduction: Many substances have been shown to benefit the bridging of neural defects through hollow conduits. Different cell populations, including Schwann cells, fibroblasts genetically engineered to overexpress Nerve Growth Factor, and olfactory epithelial neuroglia have been shown to purport a regenerative benefit through neural guidance conduits or grafts when introduced across neural defects. Cell lines of neuronal precursors have been established as a research tool to study aspects of neural development, repair, and regeneration. We sought to examine the effect of two immortalized neural precursor lines on peripheral nerve regeneration in vivo. Materials/Methods: A neural cell line derived from the mouse embryonic cerebellum (C-17.2), and a similar line derived from rat medullary raphe (RN33B) were employed. Schwann cells were harvested from neonatal Fisher rats, purified, and expanded. Each of the cell populations was then suspended in dilute (1:3) growth factor reduced matrigel/medium at a concentration of 20 million cells/ mL, inserted into medical grade silicone conduits (ID .058 in, wall thickness 0.009 in), and implanted across a 10 mm gap in the rat sciatic nerve of 175-200 g Fisher rats. Animals received either C17.2 cells (n=8), RN33B cells (n=8), matrigel only (n=9), Schwann cells (n=8) or autografts (n=8). Animals were tested for functional recovery on a weekly basis starting at 6 weeks postoperatively, and sacrificed at 10 weeks. The implants were harvested, and in the case of a neural bridge, the distal stumps were fixed in EM grade glutaraldehyde for histomorphometric analysis. Results: Fourteen out of 16 animals receiving neural cell lines had conduits with no neural regenerate, and two animals contained a pinpoint cable, with no significant axonal bridging. In the group receiving matrigel alone, all animals formed neural cables through the silicone conduits. Likewise, in the group receiving syngeneic Schwann cells, cables were universally formed, save one animal which appeared to have developd a postoperative wound infection. Autografted animals all contained viable, regenerated axons in their distal sciatic nerves. Functional analysis revealed improved sensory recovery in the matrigel only, Schwann cell, and autografted groups as compared with the neural cell line groups. Conclusion: There is no discernable benefit to the presence of immortalized neural precursor lines in the bridging of 10 mm rat sciatic nerve gaps. They may exhibit an inhibitory effect on regeneration across gap lengths ordinarily permissive to regeneration.