The secreted glycoprotein reelin is thought to control neuronal migration in the developing vertebrate CNS by directly acting on neurons. Now, Hartfuss et al. report that reelin may also affect neuronal migration by regulating radial glial cell morphology in a region-specific manner (see p. 4597). These cells are characterised by long radial processes that facilitate the migration of newborn neurons in the developing cerebral cortex. The authors found that in reeler mutant mice (which lack reelin), fewer neurons than normal had radial processes in the ventricular zone of the cortex, but not elsewhere in the brain. Moreover, in vitro, reelin increased levels of brain lipid-binding protein (which possibly influences radial glial cell morphology) and the extension of the processes of cortical, but not of basal ganglia-derived,radial glial cells. These effects, the authors show, are due to reelin signalling directly to radial glia.