Apoptosis of ameloblasts were examined by the TdT-mediated dUTP-biotin nick end-labelling method and electron microscopy 8 h after injection of colchicine. The results showed that extensive apoptosis occurred in ameloblasts of secretion to maturation zones. To determine the possible involvement of stimulators in ameloblast apoptosis, Fas, Fas ligand, tumor-necrosis-factor α, and tumor-necrosis-factor receptor 1 were examined utilizing immunohistochemistry and Western blotting analysis. Only Fas was consistently detected in the secretion, transition and maturation ameloblasts and overlying enamel organ epithelia. These results suggest that ameloblasts could undergo apoptosis by colchicine and that one of the ameloblast apoptosis mediators would be the Fas receptor.