Fibroblast growth factor-2 (FGF-2) and epidermal growth factor (EGF) have both been reported to stimulate precursors in the developing CNS. To clarify these effects, we used clonal analysis to determine the lineage potential of precursors stimulated with each factor, at two stages of development. It was found that in cells isolated from the cerebrum of embryonic day 17 (E17) mice, FGF-2 stimulated both a multipotential precursor, which gave rise to neurons and astrocytes, and a committed glial precursor. In contrast, EGF only stimulated the glial restricted precursor. Thus, it appears that the multipotential cell, previously identified to be present at E10, remains selectively responsive to FGF-2, and that the EGF responsiveness observed at E17 reflects the presence of a new restricted class of precursors, rather than a switch in factor specificity of the multipotential cell.