Medulloblastoma, a common pediatric brain tumor, is a primitive neuroectodermal tumor which often displays neuronal and/or glial characteristics. We have investigated the consequences of treating cell lines derived from a human medulloblastoma with glia maturation factor-beta (GMF-beta), a protein found in mammalian brain. GMF-beta promotes growth arrest and morphological alteration of cultured glioma and neuroblastoma cells. The proliferation of medulloblastoma cells was arrested 24-48 hr after exposure to human recombinant GMF-beta. During the same period, treated cells acquired a morphology similar to that of mature astrocytes. By 72 hr, all treated cells bound an antibody against glial fibrillary acidic protein (GFAP), a distinguishing biochemical feature of mature astrocytes. Immunoreactivity was accompanied by de novo expression of GFAP mRNA. Our observations are the first demonstration of the induction of morphological and biochemical characteristics of mature astrocytes in cultured medulloblastoma-derived cells by an exogenous factor.