Spinal motoneurons have a capability to regenerate CNS-type axons after intramedullary lesions in the adult cat. Regrowing axons have been traced through CNS-type scar tissue in the ventral funiculus of the spinal cord and into adjacent ventral root fascicles. This scar tissue, which appears to support and sustain regenerating axons, has been shown to have a persistent defect in the blood-brain barrier. It has been suggested that the blood-brain barrier may play a vital role in CNS regeneration by regulating the access of blood-borne trophic factors to the lesion area. In the present study, the binding of antibodies to the human nerve growth factor receptor in the cat spinal cord was examined with immunohistochemical methods 2 days to 8 weeks after a ventral funiculus lesion. The results show that, while no neurons in the ventral horn of the control material contained nerve growth factor receptor-like immunoreactivity as revealed by fluorescence microscopy, affected motoneurons expressed nerve growth factor receptor after ventral funiculus lesion. Nerve growth factor receptor-like immunoreactivity associated to both capillaries and interstitium was present in the scar tissue. Electron microscopic examination of sections labelled with the immunogold-silver method showed that perivascular nerve growth factor receptor-like immunoreactivity was located exclusively to non-pericytic perivascular cells. These cells were abundant in the expanded capillary perivascular spaces adjacent to the traumatic lesion. Similar cells, with or without relation to blood vessels, were observed in the scar tissue and in the pia mater. In a separate set of specimens it was observed that a ventral funiculus lesion combined with ventral root avulsion, which removes denervated PNS tissue, resulted in an expression of nerve growth factor receptor-like immunoreactivity which was similar to the one observed after ventral funiculus lesion only. The results of the present study show that affected motoneurons and cells in the scar tissue express nerve growth factor receptor after ventral funiculus lesion which implies that neurotrophic factors related to nerve growth factor may be of importance for the regenerative response.