In previous studies we have demonstrated that spinal motoneurons in the adult cat can regenerate CNS-type axons through CNS scar tissue into denervated ventral roots. This scar tissue, which appears to support and sustain the growth of injured CNS axons, has been shown to have a persistent defect in the blood-brain barrier (BBB). In the present study, the binding of antibodies to nerve growth factor receptor (NGFr), laminin, collagen, and a microtubule associated protein (MAP5) was assessed with indirect immunohistochemical methods 4 days-20 weeks after a lesion in the ventral funiculus of the spinal cord. An increase in content of collagen-, laminin-, and NGFr-like immunoreactivity was observed in the scar tissue during the first 3 weeks. Although type I collagen dominated in superficial areas of the scar, type IV collagen and laminin-like immunoreactivity was observed in expanded perivascular spaces all over the lesion zone. Type IV collagen- and laminin-immunoreactive structures sometimes appeared to form strands which interconnected the ventral horn and the ventral root. Regenerating axons, as revealed by staining with MAP5 or NGFr antibodies, were observed in close association to these paths. It has been suggested that a breakdown of the BBB may play a vital role in certain types of CNS regeneration by increasing the access of blood-borne trophic factors to the lesion area. The demonstration of extracellular matrix proteins like laminin provides further evidence for the notion that the observed regenerative growth takes place in an environment that is markedly different from the normal CNS.