The distribution of calcium in the enamel organ of the rat incisor was investigated using potassium pyroantimonate for ultrastructural localization of calcium. Substantial amounts of precipitate occurred in the intercellular compartment of the enamel organ and modest deposits were observed in specific organelles of the secretory ameloblast. Mitochondria, nuclei, granular endoplasmic reticulum, Golgi vesicles and secretory granules consistently contained small deposits of pyroantimonate. Complexing of calcium by the pyroantimonate was confirmed by EGTA decalcification and scanning electron microscope energy dispersive X-ray analysis. The observed distribution is discussed in light of potential for an intercellular pathway of calcium transport as well as controlled movement of the ion along the synthetic and secretory route followed by organic components of enamel.