Human oligodendroglioma cells cultured in serum-supplemented media lose their oligodendrocytic antigenic markers and acquire astrocytic markers. However, after reimplantation in rodent brain, these cells re-express oligodendrocytic markers. This switch in human oligodendroglioma cell phenotype could result from the interplay of different stimuli in vitro vs in vivo The in vitro differentiation into astrocytes might result from non-physiological culture conditions. It is shown that human oligodendroglioma cells behave in a way similar to that of rodent bipotential 0-2 A progenitor cells which can be driven to differentiate into either oligodendrocytes or type 2-astrocytes depending on the culture medium. Indeed, in serum-supplemented medium, human oligodendroglioma cells proliferated and expressed the GFAP astrocytic marker. In chemically defined medium containing insulin, human oligodendroglioma cells were quiescent and expressed the OI oligodendrocyte-specific marker. In both media, human oligodendroglioma cells expressed the A2B5 membrane marker as well as the SCIP transcription factor specific of 0-2 A cells, further confirming their oligodendrocytic origin. Replacement of insulin by platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF), known to maintain 0-2 A progenitors in a proliferative state, stimulated DNA replication of human oligodendroglioma cells cultured in chemically defined medium.