We have investigated the factors controlling both the morphological transformation of glial processes into endfeet and the deposition of extracellular matrix molecules into the overlying basement membrane by destroying meningeal cells over the hamster cerebellum by 6-hydroxydopamine administration on the day of birth. We report that within 24 h of destruction of meningeal cells, the concentrations of fibrillary collagens types I, III and IV in the glia limitans externa and the associated basement membrane molecules laminin, collagen type IV, and fibronectin are greatly diminished, resulting in the development of focal gaps in the basement membrane. The immunohistochemical integrity of the basement membrane is restored within 3 days over those surfaces of the folial apices where meningeal cells reappear. Likewise, the fibrillary collagens of the associated interstitial matrix are re-established in the same amounts as in controls. However, meningeal cells remain permanently absent from fissures and all extracellular matrix molecules tested disappear from rostral cerebellar folia covered by the anterior medullary velum. Moreover, the glial endfeet make up the superficial glia limitans only on folial apices, while they disappear from the fissural surfaces. In primary cultures, meningeal cells produce the fibrillary collagens type I, III, and VI, and the matrix molecules fibronectin and laminin, collagen type IV, nidogen, and heparansulphate proteoglycan. These findings indicate that meningeal cells (i) produce molecular components of both the interstitial matrix and the basement membrane, and (ii) are involved in the morphological transformation of glial fibres into the endfeet which constitute the superficial glia limitans.