Neocortical neuronogenesis occurs in the pseudostratified ventricular epithelium (PVE) where nuclei of proliferative cells undergo interkinetic nuclear movement. A fraction of daughter cells exits the cell cycle as neurons (the quiescent, or Q, fraction), whereas a complementary fraction remains in the cell cycle (the proliferative, or P, fraction). By means of sequential thymidine and bromodeoxyuridine injections in mouse on embryonic day 14,�we have monitored the proliferative and postmitotic migratory behaviors of 1�and 2�hr cohorts of PVE cells defined by the injection protocols. Soon after mitosis, the Q fraction partitions into a rapidly exiting (up to 50�μm/hr) subpopulation (Q_r) and a more slowly exiting (6�μm/hr) subpopulation (Q_s). Q_r andQ_s are separated as two distributions on exit from the ventricular zone with an interpeak distance of ∼40 μm. Cells in Q_r andQ_s migrate through the intermediate zone with no significant change in the interpeak distance, suggesting that they migrate at approximately the same velocities. The rate of migration increases with ascent through the intermediate zone (average 2–6.4 μm/hr) slowing only transiently on entry into the developing cortex. Within the cortex, Q_r andQ_s merge to form a single distribution most concentrated over layer V.