Medulloblastomas are primitive neuroectodermal tumours that are thought to arise from multipotent precursor cells in the cerebellum. Medulloblastoma cells may be undifferentiated or exibit glial, neuronal or ependymal characteristics, suggesting that they may conserve their ability to differentiate in appropriate circumstances. Medulloblastoma cell lines may thus provide models to study the commitment and differentiation of multipotent CNS progenitor cells. A human medulloblastoma cell line, DEV, has previously been shown to differentiate in an astrocytic pathway after infection by the retrovirus HTLV-1. In this study immunofluorescence flow cytometry shows that cholera toxin β subunit (CTβ), which binds to the ganglioside GM1, induces a twofold increase in the number of DEV cells differentiating towards a neuronal pathway, as shown by the increased proportion and labelling intensity of cells stained by an anti-neurofilament antibody. Immunocytochemistry shows that after 3 days in culture with CTβ, DEV cells develop processes which stain positive for neurofilaments and MAP-1. This suggests that CTβ induces DEV cells to express a more neuronal phenotype.