The organic matrix of enamel presents two distinct forms within each prism of developing crystals. The first, which is present prior to crystal formation, is homogeneous in appearance and is confined mainly to recesses at the apical end of the ameloblast. The second, in the form of an elliptical tubule of increased electron density, surrounds each crystal. The tubule is apparently organized at the time of crystal formation, for it is not seen earlier. The absence of crystals within tubules near the cell in glutaraldehyde-fixed material is incompatible with observations made on osmium-fixed tissue, where all tubules surround crystals regardless of their distance from the ameloblast. Sequential fixation in osmium, followed by glutaraldehyde, improved the ease of tubule visualization, and all tubules contain crystals regardless of their proximity to the cell. After EDTA demineralization the relatively dense elliptical tubule persists even though the hydroxyapatite crystal is removed.