Newborn ferrets were inoculated with Mink Enteritis virus (parvovirus). They developed a cerebellar hypoplasia and presented severe ataxia. Electrophysiological study by intracellular recordings in the cerebellar cortex demonstrates that in these ferrets, like in other mammals, Purkinje cells deprived from granule cell input during development remain multiply innervated by climbing fibers in the adult.