A scanning electron microscopic cast technique was used to determine the nature of the canalicular system in human cellular cementum. Prior light microscopic observations suggested the presence of two distinct types of lacunae: bonelike and a large irregular type generally confined to the interradicular region. Only the bone-like lacunae were visualized in the SEM cast preparations. The canalicular system associated with the bone-like lacunae was usually continuous from the surface of the dentin to the surface of the cementum in newly-erupted teeth. Casts having a sponge-like configuration were observed near the cementodentinal junction in some of the specimens from the interradicular region. The presence of these casts could not be predicted from prior light microscopic observations and it was concluded that they may represent infiltration of hypomineralized matrix rather than lacunae.