After transection of adult mouse sciatic nerve, the expression of a chondroitin sulphate epitope recognized by the monoclonal antibody 473-HD (mAb 473-HD) was found to be up-regulated. The epitope was localized immunocytochemically mainly in Schwann cell basal laminae and, more weakly, also in the endoneurium. In cultures of mouse dorsal root ganglion cells, Schwann cells expressed high levels but fibroblasts only low levels of the epitope. To identify the molecule(s) carrying this chondroitin sulphate epitope, human sciatic nerves were extracted with phosphate-buffered saline and shown to contain two chondroitin sulphate proteoglycans of apparent molecular weights of 130 and 900 kDa. The 900 kDa and, more weakly, the 130 kDa proteoglycan were reactive with mAb 473-HD, which was found to recognize chondroitin-6-sulphate as epitope. Following chondroitinase ABC treatment of the 130 kDa proteoglycan, a core protein of ∼45 kDa was seen and shown to react with polyclonal antibodies against the chondroitin-dermatan sulphate proteoglycan decorin from human fibroblasts. Chondroitinase ABC treatment of the 900 kDa proteoglycan yielded a core protein with a molecular weight of ∼400 kDa that was recognized by polyclonal antibodies against recombinantly expressed fusion proteins from human versican. After transection of adult mouse sciatic nerves, the distal nerve stumps showed up-regulation of the chondroitin-6-sulphate epitope of the 900 kDa proteoglycan, whereas the core protein of this proteoglycan did not show any detectable change in the level of expression. In contrast, the core protein of the 130 kDa proteoglycan was up-regulated in expression. These observations suggest that versican- and decorinlike molecules may contribute to successful regeneration in the peripheral nervous system of mammals.