Six isozymes of protein kinase C were analysed in the rat cerebellum using immunohistochemistry. The results revealed a non-uniform distribution of protein kinase C delta among Purkinje, basket, and stellate cells. Serial-section mapping of the delta immunoreactivity revealed that (i) the number and intensity of labeled Purkinje cells increased from rostral to caudal while labeled basket-stellate cells decreased caudally; (ii) the majority of Purkinje cells were labeled in the nodulus, flocculus, and paraflocculus while the anterior lobules were mostly negative; and (iii) labeled Purkinje cells formed distinct parasagittal bands in lobules 6-9 of the paravermis and vermis. The banding of protein kinase C delta within subsets of Purkinje cells suggests units of cerebellar circuitry with specific signaling properties through protein phosphorylation. The visual-vestibular regions of the cerebellum contained the highest amount of the isozyme.