High resolution electron microscopy has provided precise measurements of human enamel crystallites from the first stages of enamel development to the last stage of maturation, through counting of lattice planes and statistical analysis. Thickness and width measurements of human enamel crystallities in their mature stage are 263 A (21.9 standard error) and 683 A (134 standard error), respectively. The growth curve of enamel crystallites was drawn, the increase in the number of lattice planes in the course of enamel development was demonstrated. Fusions and dislocations related to the maturation process were visualized and discussed. Difficulties linked to the use of ultrastructural techniques were mentioned. The question of the organic stroma of the crystals remained unsettled.