The silicone chamber model permits the investigation of the cellular and molecular events underlying successful regeneration of the rat sciatic nerve across a 10 mm gap. When 25 l chambers are implanted prefilled with phosphate-buffered saline (PBS), it takes 5–7 days before sufficient fibrin matrix (derived from plasma precursors) accumulates naturally to form a complete bridge across the chamber gap; at 1 week postimplantation, cellular migration into the matrix from the nerve stumps is just beginning. The temporal progress of regeneration might be stimulated if a fibrin matrix, conductive to cell migration, was provided to the nerve stumps at or shortly after the time of chamber implantation. To test this hypothesis, chambers were prefilled, at the time of implantation, with different preparations of homologous plasma. A solution of 90% platelet-free plasma dialyzed against PBS (DP) formed a fibrin matrix by 24 hours postimplantation that, like the naturally formed matrix, had a predominantly longitudinal orientation. The temporal progress of regeneration was stimulated in the DP-prefilled chambers; at 17 days postimplantation, the extents of Schwann cell migration and axonal elongation were significantly greater than in the control system. In contrast, prefilling chambers with either non-citrated plasma or DP + calcium resulted in the generation of a matrix within 8 minutes that was composed of randomly oriented fibrin polymers. These matrices significantly retarded the progress of regeneration.