Following transplantation of cultures of CNS glia containing leptomeningeal cells into ethidium bromide-induced demyelinating lesions, meningeal cells adopt either compacted or diffuse arrangements. The compacted arrangements involved no interactions with other cellular components of the remyelinating environment, and were particularly prominent following transplantation of cultures containing a high proportion of fibronectin-positive meningeal cells. The diffuse arrangements involved interactions with astrocytes, Schwann cells and endothelial cells, and contributed to a fragmented appearance of the lesion. Such observations indicate that meningeal cell contamination should be avoided when attempts are being made to repopulate glial-deficient lesions in the CNS by transplanting central glial cells, since their effect is to partition the glial environment.