Enamel tufts were exposed after decalcification of the enamel matrix and their fine structures and immunocytochemical characteristics were examined. Under the binocular microscope and the scanning electron microscope (SEM), enamel tufts appeared as corrugated ribbon-like structures located on the dentine parallel to the tooth axis. SEM observation disclosed enamel tufts as bundles of well extended tubular structures with cross striations attributable to hypocalcified enamel sheaths. Plate-like structures were observed at the center of enamel tufts, where they ran parallel to the enamel tufts. Under the transmission electron microscope (TEM), the plates of tufts revealed their origin in the superficial layer of the dentine, penetrating the hypercalcified zone adjacent to the dentine-enamel (D-E) junction, and then reaching the tuft region. The plates of tufts ran mainly along the enamel sheaths and partially across the prisms in the tuft region. THe protein-A-gold technique revealed an intense immunoreactivity for amelogenin over the superficial layer of the dentine, but over the enamel prisms in the tufts nor over the plates of tufts. The immunoreactivity for 13-17 kd protein was detected over the filamentous structures closely associated with the enamel sheaths in the enamel tuft. Thus our study disclosed that enamel tufts consist of both well extended hypocalcified enamel prisms and plates of tufts. The major organic component of the enamel tufts is suggested to be 13-17 kd protein rather than amelogenin.