We examined the developmental expression of PC3, a nerve growth factor (NGF) early induced gene in PC12 cells, in the rat central nervous system (CNS) and we found that it represents a molecular marker of ongoing postmitotic neurons production. PC3 is initially expressed in the ventral quarter of the neural tube, at the level of the presumptive cervical spinal cord just where and when (10-11 days post coitum (dpc)) the motor neurons are arising. Subsequently, the appearance of PC3 expression follows a ventro-dorsal and a rostro-caudal gradient in the spinal cord and a caudo-rostral gradient across the brain vesicles that coincide, both spatially and temporally, with the gradients of neurogenesis described in the literature. As in PC12 cells, PC3 mRNA expression appears to be transient in vivo. In all regions of the CNS, it is restricted to the ventricular zone of the neuroepithelium, while neuronal precursors cease to express PC3 as they migrate to the mantle zone. Moreover, PC3 mRNA disappears from the various regions of the CNS as neurogenesis ceases.