In the nerve regeneration silicone chamber model, the regenerate which forms across a 10-mm gap between proximal and distal nerve stumps is a monofascicular structure with an outer perineurial-like cell sheath. Recent work has provided indications that the geometry of the regenerate within a silicone chamber can be altered by experimental modifications of the chamber matrix. In the present study we modified the standard silicone chamber into a two-compartment chamber by inserting a 6- or 10-mm-long siliconized nitrocellulose strip in order to obtain two separate regenerates. Light microscopy 16 days after implantation revealed that two separate nerve structures had formed, one on each side of the nitrocellulose partition and adjacent to it, and each with its own perineurial-like cell sheath. In chambers with 6-mm-long strips a monofascicular regenerate started from the proximal stump and divided into two separate structures as it approached the proximal end of the strip: the two fascicles joined again into a monofascicular structure in the distal portion of the chambers. The new two-compartment silicone chamber model appears suitable for future examinations of experimental fasciculation. In addition, the nitrocellulose partition should allow one to study specific effects of growth factors on axonal regeneration in vivo, as growth factors bind strongly to untreated nitrocellulose while retaining their biological activity.