The present descriptive study shows the expression pattern of an mRNA, IIIG9, whose most striking expression is seen along the lining of all four ventricles of the adult rat brain. Lower levels of expression are evident in other areas of the brain, notably in cortex, hippocampus, and various thalamic, hypothalamic and brainstem nuclei where it seems to be primarily neuronal, with little or no expression in white matter tracts. However, expression in cells on both sides of the basement membrane of the ependyma suggests expression in other cell types such as astrocytes, neuroblasts and putative precursors (subependyma), as well as ependymal cells and tanycytes. In the periphery, ovary had an expression level similar to the brain, whereas testes had a much higher level of expression.