A quantitative analysis was made of alterations in the dentritic organisation of Purkinje cells in the cerebellum of the adult rat following the administration of the degranulating agent, thiophene. This substance completely eliminated the granule cell population in a number of regions of cerebellar cortex. Purkinje cell dentdritic trees in these regions were markedly reduced in size when compared with control cells and provided evidence for a non-random loss of dentritic segments. Other dendritic abnormalities were noted. These results were discussed in relation to current theories of neuronal maintenance, and the feasibility of using toxic degranulating agents, such as thiophene, was considered.