The kinetics of postnatal cerebellar neurogenesis in chicks was studied by ³HTdR autoradiography. Results suggest that DNA synthesis occurs mainly in the external granular layer. After a premigratory period of 2 to 3 days in the external granular layer, cells begin to migrate and give rise to nuerones of the molecular and internal granular layers and to glial cells of the white matter. During the premigratory period most cells from the external granular layer are dividing; however 10 to 15% of cells seem to be able to migrate without any previous division. In the chick, a precocious species, postnatal cerebellar neurogenesis seem to pro-ceed at a slower rate than in altricial species such as mice and rats.