Ependymal cells lining the cerebral ventricles are divided into two types; ependymocytes and tanycytes (Garcia et al 2001). Ependymocytes are columnar cells that are ciliated or non-ciliated, whereas tanycytes have processes projecting into the hypothalamus. Feeding-related hormones such as insulin and leptin are present in the cerebrospinal fluid (CSF) (Baskin et al 1983). Their uptake into ependymal cells may mediate actions on brain areas responsive to changes in energy balance. To determine whether ependymal cells possess appropriate transport or signalling molecules we have investigated whether they contain insulin receptors, insulin, and GLUT 4 by immunocytochemistry in the rat. Adult rats were deeply anaesthetised with a lethal dose of pentobarbitone sodium (80mg/kg), and killed and fixed by transcardial perfusion using 4% paraformaldehyde. The brain was removed and appropriate regions processed immunocytochemically with standard immunohistochemical methods and visualised using confocal microscopy. Insulin receptor and GLUT 4 immunoreactivity (ir) were colocalised on the apical surface of vimentin-positive ependymal cells in the dorsal part of the third ventricle. Insulin receptor ir was located on the base of cilia whereas GLUT 4 was distributed throughout the cilia. We also identified a distinct subtype of ciliated ependymocytes immunoreactive for insulin but negative for insulin receptor. Insulin receptor ir and GLUT 4 ir were also located in glial cell end feet, possibly tanycytes, terminating around blood vessels within the arcuate nucleus, and GLUT 4 was also colocalised with vimentin marking the β 2 tanycytes in both cell bodies and processes. Thus ciliated ependymocytes can be subdivided into two groups; the presence of the insulin receptor and GLUT 4 on the surface of one subtype suggests these cells require insulin to take up glucose from the CSF. Immunoreactivity for insulin in the second subtype suggests these cells may produce insulin, however this will need further confirmation. This insulin could be required by the insulin receptor-containing cells to enable the uptake of glucose, providing energy for the beating of cilia. The presence of insulin receptors and GLUT 4 within tanycytes projecting to the arcuate nucleus suggests a regulatory role for tanycytes in signalling changes in CSF glucose and insulin to feeding-related areas in the hypothalamus.