Abstract Although long known to be a liver-derived fetal plasma glycoprotein, fetuin has morerecently been shown to be present in sub-populations of neurons in the developing nervous systemof a number of mammalian species. We have extended these observations to examine the fetuinimmunoreactivity (IR) in developing rat retina and cerebellum. Fetuin–IR was first seen in theretina on embryonic day (E)19 in a sub-population of cells in the retinal ganglion cell layer and asmall proportion of cells in the neuroblastic layer. The proportion of cells in the ganglion layerexhibiting fetuin-IR increased until postnatal day (P)10 when all cells in this layer were stronglyimmunoreactive. From P14 onwards fetuin–IR was absent or very weak and restricted to a smallproportion of ganglion cells. In the developing cerebellum, the outer and inner granule cell layers,the deep nuclei and cells in the sub-cortical white matter exhibited fetuin–IR from E19 to P10.There was little fetuin–IR in the cerebellum at ages P14 and older, and Purkinje cells did notexhibit fetuin–IR at any time. The results show that fetuin appears in many neurons in the retinaand cerebellum that are differentiating during the period from E19 to P10. The concentration offetuin in cerebrospinal fluid is at its highest in this same period which suggests that somesub-populations of neurons could obtain fetuin from extracellular fluid during this period ;however, the lack of fetuin–IR in other neuronal populations suggests that fetuin uptake is not ageneral property of developing neurons.