New ultrastructural alterations of the ependymal cells in the altered container model of experimental feline hydrocephalus are described. These include half desmosomes and a basal lamina on the apical surface of the ependymal cells, punctate adhesion-like structures between intraventricular mononuclear cells and the apical surface of the ependymal cells and unusual distortion of the ependymal cells. The significance of these previously unreported morphological alterations is unknown.