The developing chicken cerebellum contains two forms of the plasma membrane-associated actin-binding protein spectrin. The brain form, alpha gamma-spectrin (fodrin), is expressed constitutively in all neuronal cell bodies and processes during all stages of cerebellar morphogenesis. On the other hand, the erythrocyte form, alpha beta'beta-spectrin, accumulates exclusively at the plasma membrane of the cell bodies of Purkinje and granule cells and of neurons in cerebellar nuclei, but only after these cells have become postmitotic and have completed their migration to their final positions in the cerebellum. The appearance of alpha beta'beta-spectrin coincides temporally with the establishment of axosomatic contacts on these three neuronal cell types, which suggests that alpha beta'beta-spectrin accumulates in response to the formation of functional synaptic connections during cerebellar ontogeny.