Early cortical progenitor cells of the ventricular zone (VZ) differ from later progenitor cells of the subventricular zone (SVZ) in cell-type generation and their level of epidermal growth factor receptors (EGFRs). To determine whether differences in their behavior are causally related to EGFR number/density, we introduced extra EGFRs into VZ cells with a retrovirus in vivo and in vitro. This results in premature expression of traits characteristic of late SVZ progenitor cells, including migration patterns, differentiation into astrocytes, and proliferation of multipotential cells to form spheres. The choice between proliferation and differentiation depends on ligand concentration and progenitor cell age and may reflect different thresholds of stimulation. The level of EGFRs expressed by progenitor cells in the cortex may therefore contribute to the timing of their maturation and choice of response to pleiotropic environmental signals.