TMPase and CMPase were used as lysosomal markers. Demineralized-incisor specimens were incubated for TMPase in a lead-acetate based medium and for CMPase in a modified medium where cerium was used as the capture ion. Papillary cells contained an extensive network of branched and interconnected tubular structures reactive for both TMPase and CMPase; there were some of these structures also in the endothelium of adjacent capillaries. Fine granular material was observed in these tubular structures, as well as in coated vesicles and multivesicular bodies in the papillary cells. These cytochemical results demonstrate the presence of tubular lysosomes in papillary cells, as have already been found in adjacent maturation ameloblasts. These structures may be elements of an extensive endosomal system involved in the degradation of enamel protein. These findings also support the concept that the various cells of the enamel organ constitute a functional unit.