We have examined the expression and distribution of the extracellular matrix molecule tenascin-C in and around lesions of the thoracic dorsal columns in adult rats 3 days to 8 weeks after injury, using in situ hybridization, immunofluorescence, electron microscopy and immunoelectron microscopy. Numerous tenascin-C mRNA+ cells were present in and around the lesion at 3 days; fewer were present at 14 days and almost none 30 days after injury. Most tenascin-C mRNA+ cells in the spinal cord around the lesion were GFAP+, but most of those within the lesion were not, suggesting that tenascin-C is produced in the injured spinal cord by a subpopulation of astrocytes and by other cells that invade the lesion; these cells may include meningeal cells, macrophages, and Schwann cells. From 3 to 30 days after injury, heavy tenascin-C immunoreactivity was present at the lesion site (especially transections), and there was lighter immunoreactivity around the lesion and in the degenerating dorsal column. The heaviest immunoreactivity was associated with collagen fibrils in areas of expanded extracellular space and with basal laminae (covering Schwann cells and some astrocytes) but tenascin-C was also found close to the surfaces of some OX-42 + macrophages/microglia, leptomeningeal cells, and capillaries. Neurofilament (NF)+ axons grew into the highly tenascin-C-immunoreactive lesion sites, indicating that tenascin-C does not prevent axonal growth into these areas. However, such axons were not coated with tenascin-C except where directly exposed to the extracellular space.