In this study, the author investigated cleavage-like lines on enamel surfaces to determine whether they are actually cleavages of the enamel. These cleavage-like lines lie parallel with the long axis of tooth. With no contamination, they remain dead white even years after clinical detection. The lines are clinically noticed principally in incisors and canines but they occur also in premolars and molars. In this study, enamel cleavagelike lines found in vital teeth were observed with an electron microscope. Researchers and observers commonly seem to have regarded them as physical cleavages of the enamel. Dental clinicians seem to have paid little attention to the lines. Few research reports have been published concerning these lines. The ultra-fine images show that the lines consist of hypomineralized enamel rods and interrod substance. In other words, enamel cleavage-like lines histologically are nothing but enamel lamellae. The electron microscope observations are shown below accompanied with their explanations.