PC4 is an early NGF-inducible gene, transiently expressed during the in vitro differentiation of PC12 cells toward a neuronal phenotype. By in situ hibridization analysis, we found that PC4 is expressed at high levels along the whole neural tube of early rat embryos. PC4 mRNA expression is not uniform across the wall of the neural tube, the autoradiographic signal being most intense on the ventricular layer. At later stages, when the rate of proliferation and production of postmitotic neurons decreases, PC4 gene expression also decreases and becomes restricted to the telencephalon, that is the last region to complete neurogenesis. Thus the expression of PC4 gene, although not exclusive of proliferating cells, appears to be correlated to the time span of proliferation of neuronal and glial precursors.