In order to investigate the possible influence of norepinephrine (NE) on neuronal development, the effects of neonatal NE depletion on postnatally developing cell populations were characterized in (1) the normal mouse cerebellum, and (2) a cerebellar model system with delayed germinal cell development produced by neonatal methylazoxymethanol acetate (MAM) administration. Reduction in NE content was achieved by neonatal 6-hydroxydopamine (6-OHDA) injections. In the MAM-treated groups, 6-OHDA did not produce significant changes in external germinal layer (EGL) reconstitution. In the other groups, 6-OHDA treatment produced a reduction in the vermis area, alterations in foliation, and changes in the schedule of EGL development. These results support a role for NE in regulation of neuronal development in the cerebellum.