Previous work has demonstrated that white matter in the adult mammalian CNS inhibits cell adhesion and neurite outgrowth. This phenomenon has been investigated most recently by culturing neurons on cryostat sections of the adult CNS. Employing this same technique, we have found, in accord with others, that neurons seldom adhere to or grow on central nervous system white matter but will attach and grow on gray matter. In the experiments presented here, embryonic rat hippocampal neurons were grown on cryostat sections from the adult rat CNS, in the presence of brain derived glial cocultures. It was found that the white matter in cryostat sections can be modified by interaction with medium conditioned by brain-derived glial cells. Neurons plated on sections pretreated by such media show significant increases in both attachment and neurite outgrowth. The activity contained in glial conditioned medium is likely complex in nature. While the majority of the activity can be eliminated by heat treatment and trypsinization, neural adhesion but not neurite initiation is affected by protease treatment. Therefore, cell attachment and neurite outgrowth may be regulated by different factors in the conditioned media.