Polarity is intrinsic to neuronal function. The somatodendritic domain receives and decodes incoming information and the axonal domain delivers information to target cells. Progressive loss of neuronal polarity is a major histopathological event in neural aging and neurodegenerative diseases, like Alzheimer's disease, preceding death and disappearance of nerve cells. Our laboratory is interested in the study of the pathways and mechanisms by which neuronal membrane polarity is established and maintained. Due to the lack of appropriate polarized neuronal cell lines for biochemical analysis, the molecular mechanisms underlying this phenomenon remain obscure. We use a neuronal culture system, hippocampal neurons from rat embryos, in which polarity is established in vitro, and the scientific rationale and experimental strategies proven useful in understanding the mechanisms of epithelial polarity. Here we review our own work on neuronal membrane polarity. The reader interested should consult any of the excellent reviews published recently (7,27,31,43).