This study was done in order to investigate the normal ultrastructure of well-preserved mouse spinal canal ependyma using light, scanning and transmission electron microscopy. The ependymal lining was found to consist of a simple, cuboidal epithelium essentially similar to the unspecialized cuboidal ependyma of the brain ventricles. Apart from great variation in kinociliary density, no intracellular difference was noted between the ependymal cells. In contrast to earlier findings, indications of the existence of zonulae occludentes between the apical part of the ependymal cells were observed. Our findings do not support the hypothesis of secretion or intracellular transport by the ependyma, or that the ependyma constitutes a significant diffusion barrier.